Strangely after Quantum, Firefox worked worse for me. It is still the case, with Firefox regularly pausing all network activity for a few seconds or even a minute, so I am stuck with websites stuck loading or video stuck loading for a decent amount of time. The UI and everything functions, it is just the network communicating that is stuffed, so anything that requests something has to wait until Firefox's network part decides to respond. I am used to it now, but this happened when Quantum came out and has remained the same for me since.