Two monitors, different DPI - not scaling, Windows 8.1

[yaqwsx]

Hello,

in my Laptop I have high DPI display. I want to use external monitor with the standard, low, DPI. When I drag e.g. explorer to the external monitor, it gets scaled down properly. However some programs - namely Visual Studio, Firefox or the property dialog does not. This makes them useless.

I remember I tried this when my laptop was new and Firefox used to scale down properly. What could have changed? How can I fix it?

EDIT: I've just looked to the Process Explorer and both - FF and VS should be per-monitor aware. Also the main panel doesn't scale properly...

 

[yaqwsx]

I've just observed a weird thing - two windows of the same app (Foxit reader) and one is scaled down properly and the other isn't. When looking to the Process Explorer, one is child of explorer.exe running under schvost and the other is child of thunderbird running directly under explorer. What's happening?