1854862 - CSS hover flickers when Firefox windows are open on 2 separate macOS Spaces (virtual desktops)

Status: UNCONFIRMED

(Core :: Widget: Cocoa, defect, P5)

Description

[Steve Mokris]

Attachment: firefox-hover-flicker.zip

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/117.0

Steps to reproduce:

• On macOS 14.0 (23A344), launch Firefox 119.0a1
• Create a new Firefox profile
• Open this URL in 2 windows: https://developer.mozilla.org/en-US/docs/Web/CSS/:hover
• Place each window in a separate macOS Space (virtual desktop)
• Move the mouse over the example "Confirm" button

Actual results:

The hover state flickers on and off rapidly (see attached videos).

This makes it nearly impossible to use the hover-based dropdown menus present on many websites, e.g. https://codepen.io/una/pen/Gxwogy

Expected results:

I would expect the hover state to take effect when the mouse moves into the element, instead of flickering on and off when the mouse moves within the element.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Cocoa' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Stephen A Pohl [:spohl]]

Could you run mozregression to see when this started happening? If you have never run mozregression before, simply run these three commands in a Terminal window:

sudo easy_install pip
sudo python3 -m pip install -U mozregression --ignore-installed
mozregression --good 2017-01-01

A number of Firefox versions will open in succession to narrow down when this started occurring. Simply type "good" or "bad" in Terminal based on whether or not a build reproduces the bug. Once finished, please post the output from the last run. It should give a last good and first bad revision as well as a link to look at the changesets in that range. Thank you!

Comment 3

[Steve Mokris]

Thanks for your response. I've been able to reproduce the problem with a clean profile in all of these Firefox builds:

https://archive.mozilla.org/pub/firefox/nightly/2019/08/2019-08-26-19-09-04-mozilla-central/firefox-70.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2020/02/2020-02-04-21-43-24-mozilla-central/firefox-74.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2020/05/2020-05-14-21-11-14-mozilla-central/firefox-78.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2021/01/2021-01-01-21-05-16-mozilla-central/firefox-86.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2022/01/2022-01-01-09-53-22-mozilla-central/firefox-97.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2023/01/2023-01-01-09-08-04-mozilla-central/firefox-110.0a1.en-US.mac.dmg
https://archive.mozilla.org/pub/firefox/nightly/2023/09/2023-09-24-09-24-10-mozilla-central/firefox-119.0a1.en-US.mac.dmg

I did try mozregression, but it wasn't helpful in this case since there's no "last good revision" — the problem occurs in all versions of Firefox that I've been able to test. (I also tried about a dozen older builds ranging from 2017-01-01 to 2019-08-23, but on macOS 14 they all either crash on startup or render invisible windows, which seem to be unrelated problems.)

Since this problem occurs on all of the Firefox builds that I've been able to test, and since I only started noticing the problem after updating to macOS 14, I suspect that the problem may be due to OS/framework changes in macOS 14.

Comment 4

[Richard Walker]

See also bug 1856615.

After moving the window from one external display to another external display or to the MacBook's own display hovering may behave normally. Then moving the window back to the original external display, hovering is broken again!