2027440 - Expand on hover intermittently stops working

Status: RESOLVED DUPLICATE of bug 2031328

(Firefox :: Sidebar, defect, P2)

Description

[Raziel]

Hello. As stated in the recent last comment, Bug 1982129 is not fixed.

I never understood why bug reports are keeping getting "closed as fixed" when they are not so reports have to be duplicated again and again... ¯_(ツ)_/¯

Comment 2

[Kelly Cochrane [:kcochrane]]

Raziel, could you provide more info on instances where you've run into this issue. Also could you provide info from about:support here for us to investigate further?

Comment 3

[Jan Heinemeyer]

FWIW I'm seeing this exact issue on Firefox Nightly 151.0a1 (2026-04-14) on Linux/Wayland and have been seeing it for a while.

Expand on hover stops working and sidebar is either stuck in open or closed state.
If I manually open and close the sidebar (fastest way is pressing the CTRL+ALT+Z shortcut twice) it goes back to normal.
So that's my current workaround.

I can't tell if its anything in particular I'm doing that gets the sidebar stuck. Just seems to happen during normal use.

Comment 4

[Sho Tanimoto [:mojyack]]

I've been experiencing the same issue(Sway+Firefox 149), but managed to fix for my case.
Here are patches:
0001-Filter-sidebar-hover-blocker-to-only-handle-menupopu.patch
0002-Skip-synthetic-mousemove-through-Wayland-popups-with.patch
0003-Harden-sidebar-hover-blocker-against-Wayland-coordin.patch

patch 1 for the original issue.
patch 2 and 3 are fix for an issue after patch 1: tabbar briefly collapses when you open the context menu on it and then close it by left-clicking.
patch 2 and 3 work independently of each other. patch 2 is a more fundamental fix, but it may affect the entire browser. patch 3 fixes only the tabbar.

Comment 5

[Raziel]

(In reply to Kelly Cochrane [:kcochrane] from comment #2)

Raziel, could you provide more info on instances where you've run into this issue. Also could you provide info from about:support here for us to investigate further?

I'm unable to reproduce it and this happens way less often than before so it's very difficult to identify the root cause but,
that seems to always happens when:

• Rearranging tabs order.
• Moving cursor (quickly) between tabs and page content (maybe clicking on a tab while moving the cursor, or quickly clicking content after a tab change?)
• Maybe Alt tabbing? (not sure for this one).

I often use PIP to watch YT videos and often use a second FF profile for Twitch to watch stream in PIP view. (certainly not related as I think this has already happened without watching any video but ¯\_(ツ)_/¯).

Also, I noticed that when a menu or notification is opened/displayed the panel behavior is inhibited.
And when the panel broke, resizing it restore its behavior (as double clicking the "expand" button).

Hope this can help.

I sent you an email with the "about:support" report requested.

Best regards.

Comment 6

[Matt Ignaczak]

I raised the initial issue, and this is still happening on my environment as well. Still having intermittent recreation. I can't explicitly point to anything in particular causing it. Takes me about 10 mins to get into this state with regular usage (flipping between tabs, new tabs, hovering and not hovering). I usually run it windowed. Easiest way to reset it on my end is to toggle the 'expand on hover' option.

Running Ubuntu 25.10 with Gnome 49. Firefox 149.0.2
I find it can get 'stuck' in either state - expanded + collapsed.

Any other information that would help on this?

Comment 7

[Raziel]

As suggested in my previous message, it seems to always happen when (quickly) switching tab while moving the cursor.
Maybe while the tab is in a state to be moved (either in a new window or to rearrange order)?

Comment 8

[Raziel]

Few interesting things after the panel behavior break (and clicking the expand button twice to fix the panel behavior):

• The preview no longer work when hovering tabs.
• The buttons at the bottom (Chatbot IA, History, Bookmarks, etc...) disappear under the window when the panel expand.
• When disabling the auto expand panel behavior, there is a "separator" between tabs and buttons at the bottom that can be moved up and down to show more or less buttons when the panel is retracted.
  • It can also be moved when panel is expanded (which does nothing useful, even if the panel isn't wide enough to display all/every buttons) and it stay anywhere in the panel (while it go back at the bottom, to the height of the buttons, when the panel is retracted)
  • The interesting part is that there is no separator when panel auto expand behavior is enabled, but it appears after the panel breaks.
    It looks like the panel is in a dual (auto expand/fixed) state.

Comment 9

[Kelly Cochrane [:kcochrane]]

I just reproduced this finally on Ubuntu. Thanks for the info, Raziel. Going to investigate further.

Comment 10

[Raziel]

(In reply to Kelly Cochrane [:kcochrane] from comment #9)

I just reproduced this finally on Ubuntu. Thanks for the info, Raziel. Going to investigate further.

Oh, that's great! Thank you for your work.

I should have said in my last message that the buttons disappearing under the window (at the 2nd point) are under the separator that appear at the bottom of the side panel after it breaks (last point)

Comment 11

[Kelly Cochrane [:kcochrane]]

So we seem to have isolated the underlying issue. We'll now be tracking this issue with bug 2031328. Thanks again Raziel! Feel free to follow along there to see when that lands (we're hoping to land it tomorrow).

Comment 13

[Raziel]

Still happening in FF152.