Hello, This is most likely due to memory leak Common causes of this is sometimes extensions, such as popup blockers or themes or so can sometimes malfunction. Others can be because of heavy video streaming, or an overactive cache can cause it to cause these spikes. You can try disabling extensions, one by one. If it fixes it, then that is the problem. if not, you can re-enable all of them. A second way of troubleshooting is to type about:processes into the URL and see if a tab is taking up the memory spike. Next, you can also try clearing cache. It is only temporary files, and just makes pages load slightly slower, and usually isn't an issue after loading the website once. Lastly, make sure you are updated to the most up-to-date version of Firefox. Hope it helps!