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I typically use Chrome, but recently tried giving Firefox another chance after not having used it in a year or two.

It has some nice features that make it very attractive over Chrome (like better management for many tabs open at once), but I have found performance to be absolutely terrible much of the time.

I go overboard with tabs sometimes so I expect it to suck memory, but I find that even with only a few tabs open it is frequently using 10% or even up to 30% CPU on the regular Firefox process or usually the Plugin Container process.

When this happens Firefox becomes very sluggish, for example it may take a second or so for words I type to appear in a text box. This typically happens after it has been open for a while. Killing the Plugin Container process and reloading the tabs or just restarting usually makes it better but only for a while.

This is across three different computers and still seems to happen with all non-essential add-ons and plugins uninstalled. One computer is a cheap laptop but the other two are high-performance machines with fast processors and Firefox still becomes unusable. It happens with updated versions of both regular and developer editions.

There also typically aren't any obvious demanding scripts running on any of the pages.

nKn
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JaredL
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4 Answers4

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I have searched many places for a solution to this but nothing seemed to work. So I just opened the Options panel and took a look myself, like if it was the first time.

This solved it for me: Uncheck Options > Advanced > General > Browsing > "Check my spelling as I type"

Anton Flärd
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Try installing the NoScript extension for FireFox. This will give you more granular control over the often CPU-hungry client-side code that loads and keeps running long after the web page has finished downloading to your computer. The following StackOverflow article gives some more info on the benefits of client side Javascript manipulation: https://stackoverflow.com/questions/28377723/how-to-monitor-and-or-throttle-rate-limit-cpu-bandwidth-by-client-side-web-pages

eSavior
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Try to see if you face the same problem when you try to run Firefox in Safe mode. If no then one of the add ons or extensions is the cause. You will have to disable the add ons and extensions one by one and see if it improves your performance.

If however even in Firefox safe mode you are having issues then the problem will most probably be with the computer. You can try to do the following few items. The list given below is not comprehensive it will point you in the right direction.

  • Open windows task manager (Shortcut key CTRL+SHIFT+ESC), when Firefox is running and sort applications based on "Working Set (Memory)". Check what is consuming the maximum amount of RAM and see if you can live with closing that particular program. Look at the top 5-10 memory hogs and close those applications which you do not use. By default the "Working Set (Memory)" will not be available. You will have to go to View > Select Columns and then get this value.
  • Again with Windows Task Manager open sort the programs by "I/O Write (Bytes)". Look at the programs or services which are doing the most "I/O Write (Bytes)" and see if you can close them. This is especially important if you are using a SSD because of a concept called as Write Amplification. By default Windows Task manager does not display "I/O Write (Bytes)". You will have to go View > Select Columns and then get this option. Another point to look at is whether you can see the disk activity LED light up when you are using Firefox. If that is the case then there might be massive disk thrashing going on when you are trying to run Firefox.
  • Check if your HDD is Fragmented. If you are running a SSD then please be careful.
  • Check for free space on the HDD/SSD which has your page file system. It should not be getting full. If it is then see if it is possible to move Windows Paging file to a partition or HDD which has more free space and which will not fill up.
  • Check for free space on the partition where Firefox profile folder is kept.
  • Check if your CPU Fans are working fine and your CPU is not getting throttled. I have seen cases especially in old DELL laptops which would throttle CPU's. So for example if one has core 2 duos running 1.66 GHz, only one core would run on 1.66 Ghz and the other would run at 900 Mhz thus impacting the performance of the machine.

I am assuming that you have sufficient RAM on your computers, have an upto date virus definitions and firewall in place.

Amardeep
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I had the similar problem with Firefox 124.0.1 on Ubuntu 20.04. 'Isolated Web Co' process sometimes took 100%-250% CPU usage.

The problem is gone with updating Firefox to 125.0.1 version.

More details here: Firefox: "isolate+" process CPU usage 100%

Anton Samokat
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