Usually AdBlock works great. Have used it for many years across many browsers. Made a small donation to support development. But recently I noticed my laptop performance dropping. Opened Task Manager and seen that Firefox was using almost 3GB of RAM! Restarted Firefox in safe mode and problem subsided. Tested turning on each installed add-on in turn, and sure enough the problem lay with AdBlock. Now I do also have DuckDuckGo Privacy Essentials installed too, but the issue was replicated even when DuckDuckGo was disabled. So unfortunately I have to uninstall for now, but I'll be back once the issue hopefully gets sorted.