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-US build
• Set browser.search.region to US 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.newegg.com/
2. Add one item to cart
3. Check cart and proceed to checkout
4. Select "CONTINUE WITH A GUEST CHECKOUT" on authentication page
5. Use autofill feature to autofill preview and autofill the eligible fields

Expected result

• The eligible fields are highlighted when hovering over the corresponding entry from the autocomplete dropdown and after being autofilled.

Actual result

• None of the eligible fields is highlighted when using the autofill preview and autofill features.
  Adress1 field remains empty.

Regression range

• Not a recent regression.

Additional notes

• The issue is partially reproduceable in Google Chrome where Address 1 and State fields are not autofilled and 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.
Due to Bug 1820102 where the autofill preview doesn't work in State field, I can only confirm that this field is still not highlighted when autofilled.

I also tested on Windows 10 with the latest Nightly (138.0a1) on newegg.com (US) and observed that only the State field is not highlighted or previewed during autofill, while all other fields (address, city, postal code, etc.) are correctly highlighted.
This happens regardless the dynamic form support prefs.
This matches the behavior seen on newegg.ca where the Province field remains unhighlighted.
[Downloaded page](I also tested on Windows 10 with the latest Nightly (138.0a1) on newegg.com (US) and observed that the State field is not highlighted or previewed during autofill, while all other fields (address, city, postal code, etc.) are correctly highlighted. This matches the behavior seen on newegg.ca where the Province field remains unhighlighted.)

The behavior described in comment 3 is still reproducible in Nightly 140.0a1, all the fields are correctly highlighted except the State one(dropdown field). The State field is also not highlighted in Chrome.