After my browser being open for a while, usually a few hours, Firefox starts to get some major hanging in some tabs; I can have two windows open, one with a youtube video playing and another with like reddit or something else, and when browsing reddit, I get major hanging when interacting for around 7 seconds. I recorded a couple performance profiles to see what's causing it, and it seems to consistently be a very long JIT or GC call, also labelled as "Cycle Collection" in the waterfall view. I saved the profiles and I can upload them, but I'm not sure if they come with any private info so I'm reticent to add it to this thread. I've watched the Task Manager (the Firefox one and the Windows one) while this is happening and memory usage in the Windows task manager seems to rise quickly over a few seconds then suddenly drop back down. I'm not sure if that's relevant. In the Firefox Task Manager I didn't see anything particularly salient other than energy usage spiking up just after the hanging is over. This doesn't only seem to happen on Windows because it also happens on my Linux laptop occasionally as well, in a very similar manner. I didn't collect any evidence on Linux yet. This has been happening for quite a while now, on multiple versions of Firefox in a row. I'm using 79.0b3 Developer Edition right now on my Windows machine. Closing and reopening Firefox usually causes things to clear themselves out and I don't get such long hanging for a while. I would expect JIT and GC to happen in much smaller chunks to avoid hanging, it's strange that it takes that long for one call.