1957008 - Sidebar launcher expands and collapses if the mouse is moved left and right at the right time while the sidebar is placed on the right

Status: VERIFIED FIXED

(Firefox :: Sidebar, defect, P1)

Description

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Attachment: expand_collapse_sidebar.gif

Found in

• 138.0a1 (2025-03-27)

Affected versions

• 138.0a1 (2025-03-27)

Tested platforms

• Affected platforms: Windows 10x64, Ubuntu 24, macOS
• Unaffected platforms: none

Preconditions

• sidebar enabled
• vertical tab enabled
• expand on hover enabled
• sidebar placed on the left side

Steps to reproduce

1. Hover over the sidebar launcher and, after some time move the mouse right and left.

Expected result

• The sidebar launcher does not expand and collapse.

Actual result

• The sidebar launcher collapses and opens.

Regression range

• This might be a regression from bug 1950419. Before this bug, I could only see a similar issue, and I could expand and collapse the sidebar a maximum of two times. Please remove it if you feel otherwise.

Additional notes

• Attached a screen recording.
• Note that this is time-dependent because the issue does not reproduce only if the mouse is moved at the right time.
• The sidebar expands and collapses rapidly when the mouse is quickly moved away from the sidebar launcher when the expand animation starts.

Comment 1

[BugBot [:suhaib / :marco]]

:kcochrane, since you are the author of the regressor, bug 1950419, could you take a look?

For more information, please visit BugBot documentation.

Comment 3

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Attachment: expand_close.gif

I noticed this can also happen without moving the mouse left and right. Also, it seems more present when the sidebar is positioned on the right side.

Comment 4

[rohanrd]

For me it's not just left or right any movement on sidebar causes the glitch shown above. It's present equally for me on both sides. The transition shown above is worse on my system for some reason making it totally unusable.

Comment 5

[Sarah Clements [:sclements]]

(In reply to rohanrd from comment #4)

For me it's not just left or right any movement on sidebar causes the glitch shown above. It's present equally for me on both sides. The transition shown above is worse on my system for some reason making it totally unusable.

Hi, we need more information - can you tell us what version of Firefox you're on, what platform and post a video showing this happening?

Comment 6

[rohanrd]

I am on Firefox 137 and using Fedora. Here's the video https://youtu.be/KS7bxBGaOhc

Comment 7

[Sarah Clements [:sclements]]

(In reply to rohanrd from comment #6)

I am on Firefox 137 and using Fedora. Here's the video https://youtu.be/KS7bxBGaOhc

Thanks for the video. We made a lot of improvements in 138 - can you update to 138 and let us know if you still see that behaving the same way?

Comment 8

[rohanrd]

(In reply to Sarah Clements [:sclements] from comment #7)

(In reply to rohanrd from comment #6)

I am on Firefox 137 and using Fedora. Here's the video https://youtu.be/KS7bxBGaOhc

Thanks for the video. We made a lot of improvements in 138 - can you update to 138 and let us know if you still see that behaving the same way?

I had to remove the repository version from my system and install the binary for 138. I don't see this issue on 138.

Comment 9

[Sarah Clements [:sclements]]

(In reply to rohanrd from comment #8)

(In reply to Sarah Clements [:sclements] from comment #7)

(In reply to rohanrd from comment #6)

I am on Firefox 137 and using Fedora. Here's the video https://youtu.be/KS7bxBGaOhc

Thanks for the video. We made a lot of improvements in 138 - can you update to 138 and let us know if you still see that behaving the same way?

I had to remove the repository version from my system and install the binary for 138. I don't see this issue on 138.

Wonderful, thanks for confirming. I'll close this out.

Comment 10

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Attachment: left_right.gif

Hello! I can still reproduce this issue with Firefox 140.0a1 (2025-05-14) and 139.0b8 if the sidebar is placed on the right side. I can no longer see it if it is placed on the left side. Please see the attached screen recording. Reopening this.

Comment 11

[Kelly Cochrane [:kcochrane]]

I'm able to reproduce the issue when the sidebar is on the right.

Comment 13

[Kelly Cochrane [:kcochrane]]

Attachment: Bug 1957008 - Don't listen for mouse position while sidebar is animating

Comment 14

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/0397f34ffb79
https://hg.mozilla.org/integration/autoland/rev/236dc0254884
Don't listen for mouse position while sidebar is animating r=sidebar-reviewers,emilio,nsharpley

Comment 15

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/236dc0254884

Comment 16

[BugBot [:suhaib / :marco]]

Since nightly and release are affected, beta will likely be affected too.
For more information, please visit BugBot documentation.

Comment 17

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Verified fixed with Firefox 142.0a1 (2025-07-16) on Windows 10x64, macOS 14 and Ubuntu 24. The sidebar no longer expands and collapses after hovering over it or when the mouse is moved while the expand animation is in progress. This was verified with the sidebar moved to the right and left sides.