Found in

• Nightly 112.0a1

Affected versions

• Nightly 112.0a1
• Firefox 110.0.1
• Firefox 111.0b7

Tested platforms

• Affected platforms: Windows 10, macOS 13, Ubuntu 22.04
• Unaffected platforms: none

Preconditions

• Install the Firefox en-CA build
  Set browser.search.region to CA in about:config
  Save 1 or 2 addresses in about:preferences#privacy, Forms & Autofill section
  One address to be written on multiple lines such as:
  10123
  S Sheridan
  Rd

Steps to reproduce

1. Go to https://www.newbalance.ca/
2. Add one item to cart and proceed to checkout
3. Use autofill feature to preview the values

Expected result

• The values are previewed as filled in (data and yellow highlight).

Actual result

• Clicking twice in the firstname field > the firstname, lastname,city(not visible),Province(not visible), Postal Code, Phone number values are previewed, but not highlighted
• Clicking twice in the lastname field > the firstname,lastname,city,Province, Postal Code(not visible), Phone number values are previewed, but not highlighted
• Clicking twice in the Street field > the Street, email values are previewed, but not highlighted
• Clicking twice in the Email field > the Email, Street,Apartment values are previewed, but not highlighted
• Clicking twice in the Apartment field > the Apt,Street Address, Email values are previewed, but not highlighted
• Clicking twice in the Postal Code field > the Postal Code,Firstname, lastname,City, Province, Phone values are previewed, but not highlighted
• Clicking twice in the City field > the City,firstname,lastname,city,Province, Postal Code, Phone number(not visible)are previewed as filled in, but not highlighted

Regression range

• Not a recent regression.

Additional notes

• The issue is reproduceable in Google Chrome where not all the fields are previewed and none of them is highlighted.

:epopescu, if you think that's a regression, could you try to find a regression range using for example mozregression?

I've retested this issue in Nightly 125.0a1 (2024-03-04) on Windows10 x64 given that Bug 1755033 has been RESOLVED FIXED.
The fields are properly autofilled and previewed(except Phone field due to Bug 1819974), but they are not highlighted in yellow color upon action.
Attached screen recording.

I tested this on https://www.newbalance.co.uk, latest nightly 138.0a1 on Win 10 and noticed that the highlight is missing as well. While the fields are autofilled and the values are previewed correctly (except for the Phone field due to Bug 1819974), none of the fields get the expected yellow highlight.
This happens regardless of the dynamic form support prefs.

The same issue reoccurs on https://www.newbalance.ca/ in the latest Nightly 138.0a1. When previewing saved values in the address form, the highlight flickers and does not appear during preview and autofill. This issue is also reproducible in Google Chrome.
Additionally, while the complete address saved in Preferences is autofilled, the autocomplete suggestions dropdown does not appear, causing the City, Province, and Zip Code fields to remain hidden.