When this issue happens can you go to about:memory and do measure and save report? make sure to check anonymize. Post it here/ some paste service. Also minimize memory usage can reduce RAM usage for that moment.

Did the report. https://pastefs.com/pid/267208 I watched 3 episodes of Simpsons and did the report during third episode. RAM of main firefox instance was around 1GB at that time.

https://pastefs dot com/pid/267208 Watched 3 episodes of Simpsons and did the report during episode 3. RAM of main firefox instance was around 1GB at that time. Tried to post it two times already but didn't see my answer, so don't know if link gets blocked. But the json is to big for pastebin.

Sorry, it's not the main instance/process, it's the instance/process for Web Content thats so big.

Webextension processes "Unused bytes in all runs of all bins for this size class" has max usage, not webcontent.

To check if this is website/ js issue, when this issue happens, press f12, select memory from top and click the little camera icon. It'll show current ram usage by js.

Are you sure? Because the PID of the overloaded process in Taskmanager is the same as the PID for Web Content in the memory report. I did what you wrote and the biggest part is array buffer under objects. Here are two screenshots, one before and one after saving memory usage. https://ibb.co/3WwdDtw https://ibb.co/fCX4j91 And another measure report, don't know if it helps https://pastefs.com/pid/267495