The second part of bug 1899346 is to hide the tabs toolbar and move the red/yellow/green window controls into the nav toolbar per the spec. We'll need to make sure this looks okay across all platforms. I don't think this bug is dependent on bug 1899346 but its probably worth checking in with sfoster this.

One fun thing here is that window activeness normally changes the background color (edit: was "background title", I typoed) of the titlebar (and thus tabstrip). And the address bar / navbar is... not prepared for this. I suspect this isn't fully specced - especially as on e.g. Linux the background colour is controlled by the OS theme so is not predictable.

Yeah I think it'd make sense to treat the toolbar like a titlebar in this case...

(In reply to :Gijs (he/him) from comment #1)

One fun thing here is that window activeness normally changes the background title of the titlebar (and thus tabstrip). And the address bar / navbar is... not prepared for this. I suspect this isn't fully specced - especially as on e.g. Linux the background colour is controlled by the OS theme so is not predictable.

When you say "changes the background title" can you clarify? I see that the inactive windows title/toolbar/tabstrip/buttons are lightly grayed out (on macOS system theme). Is there something else happening? A screenshot would be helpful.

Sure. Notice in this screenshot that the active (bottom) and inactive (top) window have different background and foreground colours in the titlebar. They are different shades of grey on Windows. We have a bug on file (bug 1704131) that the difference is too subtle; this is a bit of a usability issue because of course, if you're typing or otherwise interacting with stuff (and not the kind of person who maximizes all their windows on a single screen) then knowing which window has focus (is active) is kind of important.

The default state on Linux is that we use the OS-defined colours in this case, which are more significantly different.

On Windows, the same behaviour can be turned on behind an about:config pref. bug 1851155 is on file about potentially making that the default behaviour. I'll attach a screenshot of that next.

Edit: Oh, and notice that the navbar styling is currently identical between the active/inactive windows.

Because it's an about:config pref (which I think is not exposed anywhere in the UI?) we probably don't need to spend a lot of time on this configuration on Windows - but we'll need to support the equivalent on Linux, and even the different shades of grey on Windows are likely to require additional styling work.

I'm not familiar off-hand with how this is expressed in CSS; if we're lucky it's a bunch of variables that we can "just" update in the "right" circumstances; if we're less lucky it'll need more substantial changes.

Depends on D217161

:mconley, with your recently re-acquired CUI/tabbed-browser context, would you be able to provide some feedback on this WIP patch? ISTM we can either do this entirely with CSS, entirely with the existing CSS but moving elements around, or some combination of both. Also, :dao - at the risk of inviting too many cooks into the kitchen - do you have thoughts on how we want this to happen?

(In reply to :Gijs (he/him) from comment #5)

Because it's an about:config pref (which I think is not exposed anywhere in the UI?) we probably don't need to spend a lot of time on this configuration on Windows - but we'll need to support the equivalent on Linux, and even the different shades of grey on Windows are likely to require additional styling work

High Contrast Mode also does this on Windows, and we do care about that, right?

I'm not familiar off-hand with how this is expressed in CSS; if we're lucky it's a bunch of variables that we can "just" update in the "right" circumstances; if we're less lucky it'll need more substantial changes.

Yes, these are the ActiveCaption / CaptionText / InactiveCaption / InactiveCaptionText system colors.

(I responded with some feedback in Phabricator, so clearing needinfo)

• Ensure we call TabBarVisibility.update when initializing with verticalTab=true
• Adjust TabBarVisibility logic so we allow for the vertical tabs case

Just adjusting the bug title as this turned out to involve tabs-in-titlebar logic changes as well as the important toolbar visibility change when going to/from vertical tabs.

Backed out for causing devtools failures in browser_aboutdebugging_devtoolstoolbox_tooltip_markupview.js

• Backout link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | devtools/client/aboutdebugging/test/browser/browser_aboutdebugging_devtoolstoolbox_tooltip_markupview.js | Uncaught exception in test bound - at chrome://mochitests/content/browser/devtools/client/aboutdebugging/test/browser/browser_aboutdebugging_devtoolstoolbox_tooltip_markupview.js:89 - TypeError: can't access property "ownerGlobal", elementForHiding is null

I can reproduce this failure locally on macOS, and it shows the same error per this part of the test which relies on the titlebar: https://searchfox.org/mozilla-central/rev/1b90936792b2c71ef931cb1b8d6baff9d825592e/devtools/client/aboutdebugging/test/browser/browser_aboutdebugging_devtoolstoolbox_tooltip_markupview.js#61,84-90

Yeah, thanks not sure how I missed this one.

Backed out for causing marionette failures on test_initialize_vertical_tabs.py.

• Push with failures

• Failure log

• Backout link

[task 2024-10-02T04:29:17.812Z] 04:29:17     INFO - TEST-START | browser/components/sidebar/tests/marionette/test_initialize_vertical_tabs.py TestInitializeVerticalTabs.test_restore_tabstrip_customizations
[task 2024-10-02T04:29:17.812Z] 04:29:17     INFO -  1727843357812	Marionette	DEBUG	Accepted connection 2 from 127.0.0.1:50064
[task 2024-10-02T04:29:17.813Z] 04:29:17     INFO -  1727843357813	Marionette	DEBUG	2 -> [0,1,"WebDriver:NewSession",{"strictFileInteractability":true}]
[task 2024-10-02T04:29:17.813Z] 04:29:17     INFO -  1727843357813	Marionette	DEBUG	Waiting for initial application window
[task 2024-10-02T04:29:17.814Z] 04:29:17     INFO -  1727843357813	RemoteAgent	TRACE	[10] ProgressListener Start: expectNavigation=false resolveWhenStarted=false unloadTimeout=5000 waitForExplicitStart=false
[task 2024-10-02T04:29:17.814Z] 04:29:17     INFO -  1727843357814	RemoteAgent	TRACE	[10] ProgressListener Setting unload timer (5000ms)
[task 2024-10-02T04:29:17.815Z] 04:29:17     INFO -  1727843357814	RemoteAgent	TRACE	[10] Wait for initial navigation: isInitial=false, isLoadingDocument=false
[task 2024-10-02T04:29:17.815Z] 04:29:17     INFO -  1727843357814	RemoteAgent	TRACE	[10] Document already finished loading: about:blank
[task 2024-10-02T04:29:17.815Z] 04:29:17     INFO -  1727843357814	RemoteAgent	TRACE	[10] ProgressListener Stop: has error=false url=about:blank
[task 2024-10-02T04:29:17.816Z] 04:29:17     INFO -  1727843357815	Marionette	DEBUG	2 <- [1,1,null,{"sessionId":"d0a6551f-b0b7-4c4b-9047-fd38e22a2f69","capabilities":{"acceptInsecureCerts":false,"browserName":"firefox","browserVersion":"133.0a1","platformName":"mac","unhandledPromptBehavior":"dismiss and notify","userAgent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:133.0) Gecko/20100101 Firefox/133.0","moz:buildID":"20241002005333","moz:headless":false,"moz:platformVersion":"19.6.0","moz:processID":1468,"moz:profile":"/var/folders/8y/lwsprh294bb8w7d_ymy6dtfw000014/T/tmp9s90txd1.mozrunner","moz:shutdownTimeout":60000,"pageLoadStrategy":"normal","timeouts":{"implicit":0,"pageLoad":300000,"script":30000},"setWindowRect":true,"strictFileInteractability":true,"moz:accessibilityChecks":false,"moz:webdriverClick":true,"moz:windowless":false,"proxy":{}}}]
[task 2024-10-02T04:29:17.817Z] 04:29:17     INFO -  1727843357817	Marionette	DEBUG	2 -> [0,2,"WebDriver:SetTimeouts",{"script":30000}]
[task 2024-10-02T04:29:17.817Z] 04:29:17     INFO -  1727843357817	Marionette	DEBUG	2 <- [1,2,null,{"value":null}]
[task 2024-10-02T04:29:17.818Z] 04:29:17     INFO -  1727843357818	Marionette	DEBUG	2 -> [0,3,"WebDriver:SetTimeouts",{"pageLoad":300000}]
[task 2024-10-02T04:29:17.818Z] 04:29:17     INFO -  1727843357818	Marionette	DEBUG	2 <- [1,3,null,{"value":null}]
[task 2024-10-02T04:29:17.819Z] 04:29:17     INFO -  1727843357818	Marionette	DEBUG	2 -> [0,4,"WebDriver:SetTimeouts",{"implicit":0}]
[task 2024-10-02T04:29:17.819Z] 04:29:17     INFO -  1727843357819	Marionette	DEBUG	2 <- [1,4,null,{"value":null}]
[task 2024-10-02T04:29:17.820Z] 04:29:17     INFO -  1727843357819	Marionette	DEBUG	2 -> [0,5,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.820Z] 04:29:17     INFO -  1727843357820	Marionette	DEBUG	2 <- [1,5,null,{"value":null}]
[task 2024-10-02T04:29:17.821Z] 04:29:17     INFO -  1727843357820	Marionette	DEBUG	2 -> [0,6,"Marionette:GetContext",{}]
[task 2024-10-02T04:29:17.821Z] 04:29:17     INFO -  1727843357820	Marionette	DEBUG	2 <- [1,6,null,{"value":"chrome"}]
[task 2024-10-02T04:29:17.821Z] 04:29:17     INFO -  1727843357821	Marionette	DEBUG	2 -> [0,7,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.821Z] 04:29:17     INFO -  1727843357821	Marionette	DEBUG	2 <- [1,7,null,{"value":null}]
[task 2024-10-02T04:29:17.823Z] 04:29:17     INFO -  1727843357822	Marionette	DEBUG	2 -> [0,8,"WebDriver:ExecuteScript",{"script":"const { Preferences } = ChromeUtils.importESModule(\n                  \"resource://gre/modules/Preferences.sys.mjs\"\n           ... guments[2];\n\n                prefs = new Preferences({defaultBranch: defaultBranch});\n                prefs.set(pref, value);","args":["sidebar.revamp",true,false],"newSandbox":true,"sandbox":"default","line":944,"filename":"../../venv/lib/python3.11/site-packages/marionette_driver/marionette.py"}]
[task 2024-10-02T04:29:17.826Z] 04:29:17     INFO -  1727843357826	RemoteAgent	TRACE	WebDriverProcessData actor created for PID 1468
[task 2024-10-02T04:29:17.827Z] 04:29:17     INFO -  1727843357827	Marionette	TRACE	[2] MarionetteCommands actor created for window id 4
[task 2024-10-02T04:29:17.864Z] 04:29:17     INFO -  1727843357864	Marionette	DEBUG	2 <- [1,8,null,{"value":null}]
[task 2024-10-02T04:29:17.869Z] 04:29:17     INFO -  1727843357868	Marionette	DEBUG	2 -> [0,9,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.869Z] 04:29:17     INFO -  1727843357868	Marionette	DEBUG	2 <- [1,9,null,{"value":null}]
[task 2024-10-02T04:29:17.869Z] 04:29:17     INFO -  1727843357869	Marionette	DEBUG	2 -> [0,10,"Marionette:GetContext",{}]
[task 2024-10-02T04:29:17.869Z] 04:29:17     INFO -  1727843357869	Marionette	DEBUG	2 <- [1,10,null,{"value":"chrome"}]
[task 2024-10-02T04:29:17.870Z] 04:29:17     INFO -  1727843357869	Marionette	DEBUG	2 -> [0,11,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.870Z] 04:29:17     INFO -  1727843357869	Marionette	DEBUG	2 <- [1,11,null,{"value":null}]
[task 2024-10-02T04:29:17.871Z] 04:29:17     INFO -  1727843357870	Marionette	DEBUG	2 -> [0,12,"WebDriver:ExecuteScript",{"script":"const { Preferences } = ChromeUtils.importESModule(\n                  \"resource://gre/modules/Preferences.sys.mjs\"\n           ... guments[2];\n\n                prefs = new Preferences({defaultBranch: defaultBranch});\n                prefs.set(pref, value);","args":["sidebar.verticalTabs",false,false],"newSandbox":true,"sandbox":"default","line":944,"filename":"../../venv/lib/python3.11/site-packages/marionette_driver/marionette.py"}]
[task 2024-10-02T04:29:17.872Z] 04:29:17     INFO -  1727843357871	Marionette	DEBUG	2 <- [1,12,null,{"value":null}]
[task 2024-10-02T04:29:17.872Z] 04:29:17     INFO -  1727843357872	Marionette	DEBUG	2 -> [0,13,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.872Z] 04:29:17     INFO -  1727843357872	Marionette	DEBUG	2 <- [1,13,null,{"value":null}]
[task 2024-10-02T04:29:17.872Z] 04:29:17     INFO -  1727843357872	Marionette	DEBUG	2 -> [0,14,"Marionette:GetContext",{}]
[task 2024-10-02T04:29:17.873Z] 04:29:17     INFO -  1727843357872	Marionette	DEBUG	2 <- [1,14,null,{"value":"chrome"}]
[task 2024-10-02T04:29:17.873Z] 04:29:17     INFO -  1727843357873	Marionette	DEBUG	2 -> [0,15,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.873Z] 04:29:17     INFO -  1727843357873	Marionette	DEBUG	2 <- [1,15,null,{"value":null}]
[task 2024-10-02T04:29:17.874Z] 04:29:17     INFO -  1727843357873	Marionette	DEBUG	2 -> [0,16,"WebDriver:ExecuteScript",{"script":"const { Preferences } = ChromeUtils.importESModule(\n                 \"resource://gre/modules/Preferences.sys.mjs\"\n               );\n               Preferences.reset(arguments[0]);","args":["browser.uiCustomization.state"],"newSandbox":true,"sandbox":"default","line":878,"filename":"../../venv/lib/python3.11/site-packages/marionette_driver/marionette.py"}]
[task 2024-10-02T04:29:17.875Z] 04:29:17     INFO -  1727843357874	Marionette	DEBUG	2 <- [1,16,null,{"value":null}]
[task 2024-10-02T04:29:17.875Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 -> [0,17,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.875Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 <- [1,17,null,{"value":null}]
[task 2024-10-02T04:29:17.875Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 -> [0,18,"Marionette:GetContext",{}]
[task 2024-10-02T04:29:17.875Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 <- [1,18,null,{"value":"chrome"}]
[task 2024-10-02T04:29:17.876Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 -> [0,19,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.876Z] 04:29:17     INFO -  1727843357875	Marionette	DEBUG	2 <- [1,19,null,{"value":null}]
[task 2024-10-02T04:29:17.876Z] 04:29:17     INFO -  1727843357876	Marionette	DEBUG	2 -> [0,20,"WebDriver:ExecuteScript",{"script":"const { Preferences } = ChromeUtils.importESModule(\n                 \"resource://gre/modules/Preferences.sys.mjs\"\n               );\n               Preferences.reset(arguments[0]);","args":["browser.uiCustomization.horizontalTabstrip"],"newSandbox":true,"sandbox":"default","line":878,"filename":"../../venv/lib/python3.11/site-packages/marionette_driver/marionette.py"}]
[task 2024-10-02T04:29:17.877Z] 04:29:17     INFO -  1727843357877	Marionette	DEBUG	2 <- [1,20,null,{"value":null}]
[task 2024-10-02T04:29:17.877Z] 04:29:17     INFO -  1727843357877	Marionette	DEBUG	2 -> [0,21,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:17.877Z] 04:29:17     INFO -  1727843357877	Marionette	DEBUG	2 <- [1,21,null,{"value":null}]
[task 2024-10-02T04:29:17.878Z] 04:29:17     INFO -  1727843357878	Marionette	DEBUG	2 -> [0,22,"Marionette:GetContext",{}]
[task 2024-10-02T04:29:17.878Z] 04:29:17     INFO -  1727843357878	Marionette	DEBUG	2 <- [1,22,null,{"value":"chrome"}]
[task 2024-10-02T04:29:17.878Z] 04:29:17     INFO -  1727843357878	Marionette	DEBUG	2 -> [0,23,"Marionette:AcceptConnections",{"value":false}]
[task 2024-10-02T04:29:17.878Z] 04:29:17     INFO -  1727843357878	Marionette	INFO	Stopped listening on port 2828
[task 2024-10-02T04:29:17.878Z] 04:29:17     INFO -  1727843357878	Marionette	DEBUG	2 <- [1,23,null,{"value":null}]
[task 2024-10-02T04:29:17.879Z] 04:29:17     INFO -  1727843357878	Marionette	DEBUG	2 -> [0,24,"Marionette:Quit",{"flags":["eRestart"]}]
[task 2024-10-02T04:29:17.883Z] 04:29:17     INFO -  1727843357882	Marionette	TRACE	[2] MarionetteCommands actor destroyed for window id 4
[task 2024-10-02T04:29:18.317Z] 04:29:18     INFO -  1727843358317	Marionette	TRACE	Received observer notification quit-application
[task 2024-10-02T04:29:18.319Z] 04:29:18     INFO -  1727843358318	Marionette	TRACE	Received observer notification quit-application
[task 2024-10-02T04:29:18.321Z] 04:29:18     INFO -  1727843358321	Marionette	DEBUG	Marionette stopped listening
[task 2024-10-02T04:29:18.321Z] 04:29:18     INFO -  1727843358321	Marionette	DEBUG	2 <- [1,24,null,{"cause":"restart","forced":false,"in_app":true}]
[task 2024-10-02T04:29:18.339Z] 04:29:18     INFO -  1727843358339	Marionette	DEBUG	Closed connection 2
[task 2024-10-02T04:29:21.057Z] 04:29:21     INFO -  Child process with id "1468" has been marked as detached because it is no longer in the managed process group. Keeping reference to the process id "1481" which is the new child process.
[task 2024-10-02T04:29:23.814Z] 04:29:23     INFO -  Child process with id "1481" has been marked as detached because it is no longer in the managed process group. Keeping reference to the process id "1488" which is the new child process.
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO - TEST-UNEXPECTED-FAIL | browser/components/sidebar/tests/marionette/test_initialize_vertical_tabs.py TestInitializeVerticalTabs.test_restore_tabstrip_customizations | AssertionError: 20 != 0 : Horizontal tab strip has 0 height
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO - Traceback (most recent call last):
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -   File "/opt/worker/tasks/task_172784279336048/build/venv/lib/python3.11/site-packages/marionette_harness/marionette_test/testcases.py", line 198, in run
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -     testMethod()
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -   File "/opt/worker/tasks/task_172784279336048/build/tests/marionette/tests/browser/components/sidebar/tests/marionette/test_initialize_vertical_tabs.py", line 193, in test_restore_tabstrip_customizations
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -     self.check_tabs_toolbar_visibilities("vertical")
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -   File "/opt/worker/tasks/task_172784279336048/build/tests/marionette/tests/browser/components/sidebar/tests/marionette/test_initialize_vertical_tabs.py", line 71, in check_tabs_toolbar_visibilities
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO -     self.assertEqual(
[task 2024-10-02T04:29:23.931Z] 04:29:23     INFO - TEST-INFO took 6078ms
[task 2024-10-02T04:29:23.965Z] 04:29:23     INFO - Application command: /opt/worker/tasks/task_172784279336048/build/application/Firefox Nightly.app/Contents/MacOS/firefox -marionette -foreground -profile /var/folders/8y/lwsprh294bb8w7d_ymy6dtfw000014/T/tmph57uhlfk.mozrunner
[task 2024-10-02T04:29:24.297Z] 04:29:24     INFO -  1727843364296	Marionette	INFO	Marionette enabled
[task 2024-10-02T04:29:25.877Z] 04:29:25     INFO -  1727843365876	Marionette	TRACE	Received observer notification final-ui-startup
[task 2024-10-02T04:29:25.934Z] 04:29:25     INFO -  1727843365933	Marionette	INFO	Listening on port 2828
[task 2024-10-02T04:29:25.935Z] 04:29:25     INFO -  1727843365934	Marionette	DEBUG	Marionette is listening
[task 2024-10-02T04:29:26.048Z] 04:29:26     INFO -  1727843366047	Marionette	DEBUG	Accepted connection 0 from 127.0.0.1:50102
[task 2024-10-02T04:29:26.076Z] 04:29:26     INFO -  1727843366075	Marionette	DEBUG	Closed connection 0
[task 2024-10-02T04:29:26.076Z] 04:29:26     INFO -  1727843366075	Marionette	DEBUG	Accepted connection 1 from 127.0.0.1:50103
[task 2024-10-02T04:29:26.206Z] 04:29:26     INFO -  1727843366206	Marionette	DEBUG	1 -> [0,1,"WebDriver:NewSession",{"strictFileInteractability":true}]
[task 2024-10-02T04:29:26.208Z] 04:29:26     INFO -  1727843366208	Marionette	DEBUG	Waiting for initial application window
[task 2024-10-02T04:29:27.760Z] 04:29:27     INFO -  1727843367760	Marionette	TRACE	Received observer notification browser-idle-startup-tasks-finished
[task 2024-10-02T04:29:27.766Z] 04:29:27     INFO -  1727843367765	RemoteAgent	TRACE	[10] ProgressListener Start: expectNavigation=false resolveWhenStarted=false unloadTimeout=5000 waitForExplicitStart=false
[task 2024-10-02T04:29:27.766Z] 04:29:27     INFO -  1727843367765	RemoteAgent	TRACE	[10] ProgressListener Setting unload timer (5000ms)
[task 2024-10-02T04:29:27.766Z] 04:29:27     INFO -  1727843367766	RemoteAgent	TRACE	[10] Wait for initial navigation: isInitial=false, isLoadingDocument=false
[task 2024-10-02T04:29:27.766Z] 04:29:27     INFO -  1727843367766	RemoteAgent	TRACE	[10] Document already finished loading: about:blank
[task 2024-10-02T04:29:27.766Z] 04:29:27     INFO -  1727843367766	RemoteAgent	TRACE	[10] ProgressListener Stop: has error=false url=about:blank
[task 2024-10-02T04:29:27.777Z] 04:29:27     INFO -  1727843367776	Marionette	DEBUG	1 <- [1,1,null,{"sessionId":"88848c39-e4b5-4d64-a54d-b11a66e65aae","capabilities":{"acceptInsecureCerts":false,"browserName":"firefox","browserVersion":"133.0a1","platformName":"mac","unhandledPromptBehavior":"dismiss and notify","userAgent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:133.0) Gecko/20100101 Firefox/133.0","moz:buildID":"20241002005333","moz:headless":false,"moz:platformVersion":"19.6.0","moz:processID":1493,"moz:profile":"/var/folders/8y/lwsprh294bb8w7d_ymy6dtfw000014/T/tmph57uhlfk.mozrunner","moz:shutdownTimeout":60000,"pageLoadStrategy":"normal","timeouts":{"implicit":0,"pageLoad":300000,"script":30000},"setWindowRect":true,"strictFileInteractability":true,"moz:accessibilityChecks":false,"moz:webdriverClick":true,"moz:windowless":false,"proxy":{}}}]
[task 2024-10-02T04:29:27.781Z] 04:29:27     INFO -  1727843367780	Marionette	DEBUG	1 -> [0,2,"Marionette:SetContext",{"value":"chrome"}]
[task 2024-10-02T04:29:27.781Z] 04:29:27     INFO -  1727843367780	Marionette	DEBUG	1 <- [1,2,null,{"value":null}]
[task 2024-10-02T04:29:27.781Z] 04:29:27     INFO -  1727843367781	Marionette	DEBUG	1 -> [0,3,"WebDriver:DeleteSession",{}]
[task 2024-10-02T04:29:27.783Z] 04:29:27     INFO -  1727843367783	Marionette	DEBUG	1 <- [1,3,null,{"value":null}]
[task 2024-10-02T04:29:27.783Z] 04:29:27     INFO -  1727843367783	Marionette	DEBUG	Closed connection 1
[task 2024-10-02T04:29:27.784Z] 04:29:27     INFO - TEST-START | browser/components/sidebar/tests/marionette/test_initialize_vertical_tabs.py TestInitializeVerticalTabs.test_vertical_widgets_in_area

Thanks for the backout. That turned out to be a failure in test_initialize_vertical_tabs.py. on MacOS, where the hidden tabstrip toolbar was confirmed to be collapsed, not displayed and yet reported height: 20 rather than the expected 0. That was a lot of redundant assertions and I was able to capture a screenshot to confirm it is in fact hidden at this point, so I just removed the height assertion.

https://hg.mozilla.org/mozilla-central/rev/82dacb5e3821