Affected versions

• 86.0b5, 87.0a1(2020-02-01)

Affected platforms

• Windows 7 -

Steps to reproduce

1. Launch Firefox, access about:preferences
2. Hover over menu options in the section + subsection;

Expected result

• hover effects do not cause elements to not be as visible;

Actual result

• blue background per available checkboxes on hover;

Regression range

• 81.0.1 is a good build, will check for an accurate range asap;

Additional notes

• attached screenshot with the issue;
• Windows classic theme selected.

Reproduced this issue on Windows 7 x64 using the latest Nightly 87.0a1, Firefox 86 beta 5, and Firefox 85.

Mozregression revealed the following pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=98f7e1355ed690af70997f036db0f0546c7962ed&tochange=cc1e3921893e658963369bdae4ab264f56474d5e

Found commit message:
Bug 1678333 - Fix checkbox and radio buttons to match Photon spec. r=desktop-theme-reviewers,ntim,dao

:cfogel, can you retest this on latest Nightly? I'm unable to reproduce this.

Sorry for the late reply.

As far as current Nightly(89.0a1(2021-04-03), the issue no longer manifests on the checkboxes.
However, the dropdown buttons still show it while the proton pref is disabled.