Font is too small on external screen

Hello,
since changing some screen settings on my Win 10 (1709, 64bit) laptop, I've been experiencing this problem: when I use a second screen (two screens, extended mode) I get that most of my applications display with a too small font size. E.g., on Firefox I have a very small font size for the File menu etc. This also happens in other applications, and also for the font size of the webpages I upload in Firefox.
Further, many programs have a scaling issue: they are invoked with fuzzy resolution (in order to increase their font), but this looks quite bad.

I don't know what caused this change in setting. I also don't know how to change it back to the original setting.

Any help?

Things like Firefox let you zoom in to get bigger font failing that you will have to change the screen resolution on that display

Hi there

on Firefox simply press CTRL + keys repeatedly until you get size you want.

Cheers
jimbo

Okay guys. I played with the settings, changed the Display setting etc. (to 125%), and changed back and forth from the main screen to the external one...I don't know how, but it's now fixed for some reason...

(Except for the font scaling/compatibility issue---which is bearable though).