This problem has been bothering me and friends for a long time. We keep hundreds of tabs open and this causes - depending on the viewed pages - very quickly high processor load with fans ramping up to max. A temporary fix is to restart the browser with all tabs frequently - which also dramatically reduces RAM use. Because only the viewed tabs in each browser window are loaded initially, that quiets things down immediately - until more pages are opened in different tabs that use tremendous resources. Like Amazon, other shopping sites, probably some hidden miners (otherwise I often cannot fathom why it would use so much cpu). I suggest an option for Firefox to halt/stop/suspend all tabs that are not currently selected for viewing. That is one tab per window. We have absolutely not the slightest need for any tab to do anything if it's not viewed. In a pinch we sometimes suspend the whole firefox process via ProcessExplorer - but sometimes it doesn't resume and of course it also halts the foreground tabs. Restarting is not always possible due to pages with logins and other customizations that disappear on reload.