To quote some relevant comments on other threads here:

> If you could grab a profile of the problem with the Firefox profiler and file a bug it would be greatly appreciated. From the sounds of it it's probably an edge-case we're not aware of where Firefox performs very poorly. The problem with this kind of things in Mozilla is that we're often blind until someone brings up the issue and notifies us.

https://news.ycombinator.com/item?id=33156379

> Here are instructions of using the profiler with just a few clicks: https://profiler.firefox.com/

https://news.ycombinator.com/item?id=33156317

I love the FF profiler. However I can't use it when the entire browser is hanging. I would need to run an external profiler on the browser itself. I will file a ticket as soon as I have any useful info... but when it's an intermittent 30-second freeze on all browser windows, it's tough to get any data on it.

Ah, that's a bummer indeed! Possibly devs can help you get more useful data if you report the bug first?

This is greatly related to the lack of per-tab sandboxing in Firefox (https://madaidans-insecurities.github.io/firefox-chromium.ht...) it's not only a security issue but a performance issue as well.