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"FirefoxCP Isolated Web Content" is slowly consuming all of my Mac's memory.

Making moves


I use the M1 MacBook air which has 8 GB of RAM. I use it with a 4k 144Hz monitor.

I was searching for a browser that can take advantage of my 144Hz monitor and run smoothly. Safari works only 72 Hz and chrome initially runs at 144Hz but gradually it becomes choppy after using it for 10 minutes. 

Firefox is the only browser that can sustain the 144Hz and everything runs very smoothly.

But here is the problem I am facing with Firefox. After 30 to 40 minutes of use, my whole laptop froze. When I checked the Activity Monitor it shows that "FirefoxCP Isolated Web Content"  is taking 10+ Gbs of memory.

Then I closed Firefox, everything goes back to normal. Then I opened Firefox again and closed all the tabs and put my MacBook to sleep. When I opened my MacBook, the laptop is already struggling to do anything. There was no tap opened and even in the laptop sleep mode"FirefoxCP Isolated Web Content" is gradually taking 12+ Gbs of memory.

I really want to use Firefox. I have tried all the browsers and Firefox is the only one that can run smoothly on my 4k 144Hz monitor.

So I am requesting you to help me solve this issue.

Thank you.


Making moves

using activity monitor, click on the firefoxCP isolated web content hogging memory and then the x. the offending tab in my case was hootsuite. told me "Gah. Your tab just crashed." It's not firefox but what is in the open tabs......

Making moves

I came to this thread because I was looking at my activity monitor and saw that there were 13 instances of "FirefoxCP Isolated Web Content" open.  I have a Mac Studio with 128 GB of Memory and the Apple M1 Ultra Chip. I also have the Apple Studio Display and 2 additional 27 in Samsung monitors. 

Currently I have 10 tabs open and Firefox is using about 7.5 GB of memory.  I was shocked.  I also have Safari open with 13 tabs and it is only consuming less than 1 GB of memory.  I am not having any issues like you describe but it seems to me that you should not have the issues with Safari that you are having.  Could this be a graphics card issue? 

Making moves

I just had this same issue. After reading some of the replies here, I realized I had TWO Firefox tabs open with two different Amazon products I was keeping an eye on. I closed those two tabs and the CPU fan of the 2017 MBP almost instantly started to calm down and the machine resumed its usually snappy response times.

Making moves

Same issue here. Firefox Isolated Webcontent process took up 8 GB of RAM:

Firefox 109.0.1 (64-Bit)

Operating System: openSUSE Tumbleweed 20230222
KDE Plasma Version: 5.27.0
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 6.1.12-1-default (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-7700K CPU @ 4.20GHz
Memory: 15.6 GiB of RAM
Monitor: Dell Inc. S2721DGF running at 144 Hz

Making moves

Same here. It immobizlsed  my new mac and my new macbook pro, both with Ventura 13.2.1.

I used to love mozilla. But I'm switching to chrome. Trouble not worth it. Thanks for the tips

Making moves

same issue regardless of operating system. FirefoxCP Isolated Web Content is using 100% CPU. It must have something to do with cross-site cookies being blocked. Either a mozilla oversight or websites trying REALLY hard to see cookies in your other sites

Making moves

Well, a single tab could easily consume 1 GB of RAM.

Trying using Google Maps for some time - zoom in/out, switch to Map/Sattelite/StreetView etc.

But it's the same in e.g. Chrome

Making moves

I have the same issue on Ubuntu and Firefox. The Isolated Web Content process appears each time I log into my bank account and disappears when I log out or delete the tab. The %CPU starts with 400% then stabilizes at 100% causing my fan to accelerate very strongly. Surprisingly this does not happen with the Brave navigator.