User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0
Build ID: 20210331215444

Settings

Win10 OS theme: Light or Dark
Nightly theme: Dark

No Proton related stuff is enabled in Nightly.

Steps to reproduce

1. Add search bar to UI.
2. Type something in the bar.
3. Use keyboard to highlight a search suggestion/history.

Actual result

The highlight colour is barely visible.
In the attached screenshot, in both before and after the 2nd result is highlighted by keyboard navigation while 4th by mouse hover.

Notes

1. Nightly's Default theme is unaffected even if OS is set to dark theme.
2. URL bar is not affected.

The bug should be first introduced by bug 1692046 when Dark and Proton Dark were separated, and went through some more iterations. Now Proton Dark replaces Dark and, iiuc, rides the train with bug 1701256, this bug will affect non-Proton users at Release 89.

:Fanolian+BMO, since this bug is a regression, could you fill (if possible) the regressed_by field?
For more information, please visit auto_nag documentation.

I think changing these vars should fix it:
https://searchfox.org/mozilla-central/rev/54f37fc1ac0f98b590af51e01ce82bb74179bf63/browser/themes/shared/urlbarView.inc.css#15-18
maybe to match vars like --lwt-toolbar-field-focus (which is what the urlbar uses) etc.

Set release status flags based on info from the regressing bug 1701256

Considering this works correctly in Proton, and Proton is being release in 89, I think this is a wontfix.