Could you link the tab unloader addon you are using, and is it compatible with new firefox?

I have exactly the same problem as the one you replied to.

It seems like some resources never get cleaned up, so if I in the span of a day open 100 tabs and close them then I will not end up with much higher memory usage than initially.

I have investigated this with about:memory and while not seeing something conclusive I did sometimes see domains taking up memory which were not loaded in any tab (ghost windows) or high amounts of memory used for "media".

I will try disabling the handful of addons I use beside uBlock Origin which is too essential to disable.