borekb said

I'm running Firefox on my laptop which is QHD+ on a small screen so the DPI *has to* be set to something like 150 or 200 %. I also have an external monitor which runs in its native FullHD resolution and 100% DPI. Windows 10 (maybe even Win 8) do support different DPIs on different screens so that's not a problem. However, when I move Firefox from the laptop display (150% DPI) to the external monitor (100% DPI), everything becomes blurry - web content but also the UI. Not sure how well it will be seen from the screenshot but here it is: http://snag.gy/Fz7ZS.jpg What is strange is that this happens even if I shut down Firefox and start it again. I would expect that the restart fixes things. Is there anything I could do to help this?

Yup blurry... Think this is not a FF issue but your setup. I think you would have to adjust your larger monitor to the correct DPI or over/under sampling via vid card program or Win10 when you share if it is possible.

If this solves your issue please let us know and mark as solved, G'luck

Nope, it's certainly a FF issue. For instance, moving Windows Explorer from one monitor to another, or changing DPIs in Windows, everything stays crisp. Firefox, on the other hand, as well as some other "legacy" Windows apps (Paint.NET, for example), have their UI blurry until the next system reboot / sign-out, sign-in.