Affected versions

• 89.0b1(2021-03-31), 88.0b2, 78.9.0esr;

Affected platforms

• Windows 10, Ubuntu 20;

Steps to reproduce

1. Launch Firefox, right click on the toolbar, select the Customize Toolbar option;
2. Press the TAB key to navigate across the listed buttons/items;

Expected result

• cycling through goes smoothly;

Actual result

• there is a visual delay with the focus ring when cycling through;

Regression range

• will check when time permits it, appears to be something old;

Additional notes

• attached a recording to illustrate the issue;
• borderline wonfix, but would improve the UX.

I've ended up with the following regression range:

• Last good revision: 4e4ea471e2d1c8db0c5f3a766bcb989bf95b76ad (2018-02-19)
• First bad revision: 861067332bac96a44bbf41ef366f58a30476057b (2018-02-20)
• Pushlog:
  https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=4e4ea471e2d1c8db0c5f3a766bcb989bf95b76ad&tochange=861067332bac96a44bbf41ef366f58a30476057b