Found in

• Firefox 110.0a1 (BuildId:20230109093059)

Affected versions

• Firefox 110.0a1 (BuildId:20230109093059)

Tested platforms

• Affected platforms: Windows 10 ARM.
• Unaffected platforms: macOS, ubuntu & Win non-arm devices.

Preconditions

1. Download and install the arm64 version of 7zip from https://www.7-zip.org/download.html
2. Create an archive and place it in a random folder.

Steps to reproduce

1. Launch Firefox.
2. Access the about:third-party page.
3. Hit CTRL + O and navigate to the folder in which the archive is present.
4. Right click on the archive.
5. Close the File Explorer and refresh the about:third-party page.

Expected result

• The 7-zip.dll is displayed and can be blocked via the about:third-party page.

Actual result

• The 7-zip.dll is displayed and cannot be blocked via the about:third-party page since the "Block this module" button is not displayed.

Regression range

• This is not a regression.

Additional notes

• The same dll can be successfully blocked while using a non-ARM Windows 10 machine.
• This is a blocker for the User-Driven dll blocking feature on Win ARM devices.
• The TestDllBlocklist_UserBlocked.dll is not displayed inside the about:third-party page on Windows ARM devices.

Attaching a screencast of the about:third-party page showing that the "Block this module" button is not displayed for the 7-zip.dll.

Also this is the raw data generated for the about:third-party page:

{ "modules": [ { "name": "7-zip.dll", "fileVersion": "22.1.0.0", "typeFlags": 4, "companyName": "Igor Pavlov", "events": [ { "processType": "browser", "processID": 8828, "threadID": 12684, "loadStatus": 0, "loadDurationMS": 0.8409895833333333 } ] } ], "blocked": [] }

After talking this over with :haik, since:

• this is going to be tricky to fix
• the behavior doesn't look incorrect to the user (it just looks like it did before user-defined third-party module blocking was enabled)
• we have a very small number of users on Windows on ARM

we're going to WONTFIX this and not claim support for user-defined third-party module blocking on ARM.