Hi, I have found the root cause of the problem. It's AMD drivers. I went for a clean uninstall in safe mode via Display Driver Uninstaller and installed AMD Crimson 16.5.2.1 (previous version), now everything is back on! Firefox is smooth, and fonts can be finally admired. See attached screenshots before and after. It's in Italian, but you can get the translated strings from pastebin or compare it to your system. FYI the version of AMD drivers that was causing the problem it's not a beta, it's the last production version I get when I select my GPU (v16.5.3). I have installed v16.5.2.1 and it's all good. Should this problem be reported to Firefox or AMD? Other browsers (Chrome) were rendering fine. Thanks for your help anyway.