2061779 - When switching tabs or clicking the mouse, the action is very slow.

Status: RESOLVED DUPLICATE of bug 2056929

(Firefox :: Tabbed Browser, defect)

Description

[:hellosct1]

Attachment: simplescreenrecorder-2026-08-07_17.50.49.mkv

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:155.0) Gecko/20100101 Firefox/155.0

Steps to reproduce:

Since the update on Wednesday the 5th—specifically the Firefox Nightly 155 update—all actions, such as mouse clicks and icon changes, have become very slow.
Even when managing to switch tabs, page loading is also very slow.

I ran performance tests with Web Performance to demonstrate the significant delay.

• Test 1 : https://share.firefox.dev/4fIFiQY
• Test 2 : https://share.firefox.dev/3RKWjST

Actual results:

Since the problem started, I have tried to fix it by:

• Updating Linux
• Repairing Firefox Nightly
• Unpinning all tabs
• Disabling and re-enabling extensions

Expected results:

All mouse clicks and navigation actions are still slow.

I ran two new tests using the web profiler:

• Test 1 : parameters Nightly : https://share.firefox.dev/45cL4pm
• Test 2 : parameters Network : https://share.firefox.dev/4594pb1

I also made a video showing the tabs already loaded, which I am sharing here.

Comment 1

[BugBot [:suhaib / :marco]]

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

Comment 2

[:hellosct1]

Additional Information

I disabled Nova and the problem is gone.
I did

about:config
browser.nova.enabled to FALSE

Comment 3

[Stephen Thompson [:sthompson]]

Thank you for posting the profiles. Sorry about that performance, it looks really painful!

I see a lot of time spent in layout for anchor positioning, which is a problem flagged and tracked in bug 2056929. I see that you have the Multi-Account Container add-on in your screenshot, so I'm thinking that may be the culprit. This is a problem specifically with the combination of Nova + container tabs. Our teams are working on fixes.

I can duplicate this bug to bug 2056929 unless you think there are additional factors that you don't see in that bug.

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Pretty sure this is bug 2056929