1970029 - Firefox 139.0.1 excessively high memory and CPU usage when loading simple pages and extensions

Status: RESOLVED INVALID

(Core :: Performance: General, defect)

Description

[Jerry]

Attachment: Screenshot 2025-06-02 232102.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:139.0) Gecko/20100101 Firefox/139.0

Steps to reproduce:

Firefox 139.0.1 is using excessive amount of memory and CPU when loading simple pages.

I have 4 tabs open, Google, Stackoverflow, Youtube, and new tab.

I have made some simple action by doing search, clicking links on these tabs, as well as opening the extension.

Actual results:

Pages sometimes takes long time to load, extension (uBlock Origin for instance) doesn't open instantaneously when it's supposed to. I can hear my CPU fan spinning when simple pages loads. It is affecting user experience.

Expected results:

It should be much faster when doing simple browsing.
There's also similar report on Mozilla Connect. https://connect.mozilla.org/t5/discussions/ff-broken-again-after-this-latest-update/m-p/97823#M38123

Comment 1

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

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

Comment 2

[Jerry]

Attachment: Screenshot 2025-06-03 232856.png

An easy way to reproduce on my machine is open one of the Google Angular element from Google search page, it would cripple Firefox completely.

Comment 3

[Monica Chiorean]

On Win11x64 using Firefox build 139.0.1 the CPU rose a bit but did not go over 80%.
Updating the component and waiting for engineering input. Thank you.

Comment 4

[Jerry]

I also just tested the same workflow that I described with latest ESR version of Firefox 128.11.0esr (64-bit) and there's no memory or CPU spike. Everything is working as intended. So it seems to only affect Firefox Desktop 139

Comment 5

[Jerry]

It seems like a Firefox config issue. I managed to solve this problem by doing a refresh.

However, this old config can still be reproduced if I open browser from another app. It seems that Windows default browser is still targeting the old Firefox browser with old configuration. It is happening even after I uninstall and reinstall Firefox.

Here is the step to reproduce:

• Open a new Firefox window. Everything is functional
• Open Notepad++
• Type a valid link like https://www.mozilla.org
• Ctrl + click this hyperlink to make it open
• Windows will take a few seconds to try to open this link.

Expected: A new tab is opened in my existing Firefox instance

Actual: I get a message saying "Firefox is already running but not responding. The old Firefox process must be closed to open a new window." See attached screenshot.

Comment 6

[Jerry]

Attachment: Firefox_process_error

Comment 7

[Bas Schouten (:bas.schouten)]

I don't see a difference between 139 and 138 locally.

Can you include a performance profile (capture a profile with http://profiler.firefox.com/) showing the issue for you on the bug.

Comment 8

[Jerry]

I couldn't reproduce it anymore and it doesn't affect 140. You can close this ticket.