Linux – Limit CPU usage for flash in Firefox

I think you can't do that. What you can do is modifying priority for user. You can do that by editing file /etc/security/limits.conf:

john hard priority 20

Sets priority for john's processes to 20 (effective after next login). 20 is lowest priority.

This way john can use 100% of CPU, but if someone else needs it, other user will immediately get it, and john's tasks will wait (or actually slow down, not stop completely).

I suspect it is either the Garbage Collector or the Cycle Collector.

In about:config change javascript.options.mem.log to true. Now notices about GC and CC should be available in the Error console (Crtl+Shift+J) If their timing and duration matcher the freezing, then this is your problem.

When I had this problem I fixed it by blowing away my Firefox profile and creating a new one from scratch. The Firefox profiles have a tendency to gather a lot of crud over time.

Even this is not a prefect solution. If you open a lot of tabs in Firefox (100+) or lots of extensions and leave Firefox running for days on end it will inevitably slow down. You will need to restart Firefox every once in a while.

If you are like me and have a tendency gather a large collection of tabs you need get around to dealing with at some point another trick I use is to set browser.sessionstore.max_concurrent_tabs to 0. This will stop Firefox from loading all the tabs of your session when starting. It will instead load them when you switch to them. I find this, plus the occasional restart of Firefox, greatly reduces the load of having a great many tabs.