I have set custom scaling to 125% from %100 just to see how it looks and Firefox did not respond very well. It rendered on top of my taskbar, I tried to fix it by maximizing the Firefox window again but it did not work. Then I set the scaling back to 100%, now it will not load at all. It does launch, I can see processes with task manager but will not load. I can get it to load only if I launch Firefox at 100% then switch to 125%, even then it won't render correctly. I get weird white bars and window draws over taskbar. I'll try to replicate the bug and get a full window screenshot. Thing I have tried so far are: -Deleting xulstore.json and local(forgot the name) -Deleting profiles completely -Uninstalling Firefox, deleting all left over files, using Bleachbit to delete cache etc. then reinstalling. -Enabling/Disabling Hardware Acceleration settings -Safe mode -Removing extensions -Assigning Firefox rendering to either CPU's graphics core and GPU. -And few more things that I cannot remember now. This was a fresh Windows 10 install, I have no antivirus or any other software installed that might interfere with Firefox. I have another PC with working Firefox, I will now try copying Firefox's files from that PC to this one but I do not think that will work, this is my last resort. Edit: Copying working Firefox files from another computer did not work. Edit 2: I found what caused the issue. I was using coloured title bars across Windows, unticking the "Show accent color on title bars" option on Windows 10 settings did the trick. Edit 3: Also found out that unticking the "Title Bar" setting from Firefox's customization menu fixes the issue. So, a combination the combination of setting custom title bar colors and merging the title bar with tabs caused the issue. Though, it still baffles me because this combination did work fine before and it still works fine on my desktop PC. I still believe scaling did the triggering.