Solution: All text in Firefox in italics

Out of nowhere, some time ago, all my (normal) texts in Firefox and Internet Explorer went italic. Meaning, every bit of text that wasn't in bold or a header went italics...
What happened was that for some reason the default Arial font went missing. Firefox and IE then automatically switched to the italics variant of the standard Arial font for displaying text in Arial. The solution is easy: copy a Arial.ttf file back into c:\windows\fonts.
I can't supply you with the file (licensing issues) but just know that it is supplied with every copy of windows. Just open up c:\windows\fonts on any PC that doesn't have the problem, copy the file Arial.ttf (Arial standard) onto an USB stick and then copy the file into the c:\windows\fonts folder of the PC that does have the problem..