topic Re: Firefox is too slow lately in Discussions

Firefox is too slow lately

Eduardo1 — Mon, 23 Jun 2025 04:01:39 GMT

Since a few weeks ago I noticed that Firefox makes my processor fan to run, then I checked with the Windows Task Manager how much processor it uses, and it uses like 30% (total, of all my 6 cores) having only one tab of Youtube open with a live stream video.

I tried with the troubleshoot mode with all extensions disabled and it was the same.

What happened in latest FF updates, that ruined FF so much?

Re: Firefox is too slow lately

tate — Mon, 23 Jun 2025 09:31:33 GMT

Many users have recently reported similar issues, with CPU usage jumping to around 30% or more even with all extensions disabled and Firefox running in Troubleshoot Mode. One of the most common culprits is YouTube’s Ambient Mode, which adds a background glow effect around the video when using dark theme. While visually appealing, this feature can significantly increase CPU and GPU usage. Turning it off often results in an immediate performance boost. Another major factor is video codec handling. Firefox sometimes uses high-demand codecs like AV1 or VP9 for video playback, which aren't always hardware-accelerated especially on older hardware. To resolve this, it’s recommended to enable hardware acceleration in Firefox settings and disable AV1 support by visiting about:config and setting media.av1.enabled to false. You can also install extensions like h264ify or Enhancer for YouTube to force the browser to use less demanding video app formats like H.264, which are easier on your CPU.

Re: Firefox is too slow lately

dada — Mon, 23 Jun 2025 09:53:50 GMT

Yes, me too. Firefox version 139.0.4 (64-Bit) is very slow and crashed today (June 23, 2025) already 3 times.
Extremely annoying :-(((

Re: Firefox is too slow lately

Eduardo1 — Mon, 23 Jun 2025 10:18:51 GMT

OK, thank you. I had both circumstances you described. I made both changes. Not let's see.

PS: still, something changed lately.

Re: Firefox is too slow lately

Agentvirtuel — Mon, 23 Jun 2025 10:43:33 GMT

Hello

Task Manager - see whether tabs or extensions are slowing down Firefox
https://support.mozilla.org/en-US/kb/task-manager-tabs-or-extensions-are-slowing-firefox
Perform actions in the Process Manager

Maybe
Reporting a Performance Problem
https://firefox-source-docs.mozilla.org/performance/reporting_a_performance_problem.html
You can add the profile URL to a bug.

Re: Firefox is too slow lately

IanC — Tue, 24 Jun 2025 05:24:38 GMT

I tried those and it didn't improve. Now 1080p videos are unwatchable, and I have to drop to 720 or 480. Something changed in the most recent update. Other browsers work fine.

Re: Firefox is too slow lately

Eduardo1 — Wed, 25 Jun 2025 04:48:36 GMT

The issue is not solved. It seems to be a bit random, because "sometimes" it doesn't use more than 2-3% (most of the time it uses over 20%).

What else to try?

Re: Firefox is too slow lately

Eduardo1 — Thu, 03 Jul 2025 07:56:24 GMT

I have noticed that the live streams videos at Youtube use a lot more processor than regular videos. Regular videos: ~10%, live streams: ~40%.

Re: Firefox is too slow lately

blakedj012 — Wed, 01 Oct 2025 09:18:22 GMT

Yes, I'm starting to hate this browser more and more. First there was the issue with pinned tabs, which thankfully has been somewhat fixed. But this lag after a while is really driving me crazy. And I think it will never change, because people have been complaining about how incredibly slow the browser is for over 10 years now.

Every time, you have to restart it after about 10 minutes just so it will load relatively quickly again. It's absolutely ridiculous compared to Chrome and other browsers. I've tried everything: using a RAM disk for the cache, disabling the cache completely—nothing keeps it performing at the same level it does right after restarting. But then again, what do you expect when you cram it full of useless features that nobody needs? I'm about to switch to a different browser.

I basically only use it because of the autocomplete feature for IDs and classes in the developer console; it finds all of them in the DOM. But otherwise, the entire style panel is so outdated and far behind other browsers that it's not really enjoyable to use. And the fact that it gets even slower over time makes it even worse. And yes, I've disabled all extensions and everything else; nothing makes it run faster. I've given it a new nickname: "Fire Slug."

Re: Firefox is too slow lately

robertgranata — Wed, 15 Apr 2026 10:12:08 GMT

Hey Mozilla Community,

Lately Firefox feels heavier than it used to, and even a single YouTube live stream can push noticeable CPU usage, which makes the fan spin like the browser is doing far more work than just playing video. It seems recent updates added extra background processes, security checks, and video handling changes that sometimes hit performance on certain systems, even in troubleshoot mode. Until it gets optimized again, some people just switch tasks or use lighter options when they mainly want streaming. If your main goal is watching streams without stressing the browser, you could also try a dedicated free streaming app like RBTV77 APK instead of keeping a live stream tab open.

Have a Nice Day!!

Re: Firefox is too slow lately

StevieB — Thu, 12 Mar 2026 10:55:52 GMT

It's been like this for a long time, and I have been reporting it for that same amount of time.

FF is just terrible now, each update seems to make it worse, even though we are told it's better !

My RAM and CPU usage sometimes is just off the scale, and I get that fed up with this program that I end up going over to Chrome.

WTF, FF used to be so great. I stand by my initial query that FF has some form of memory leak, or is it just sloppy programming? Either way it's seriously S L O W

Re: Firefox is too slow lately

thecassert33 — Fri, 20 Mar 2026 16:44:02 GMT

Switching to Opera..FF sucks ass now!!