http://wiki.winehq.org/FAQ#head-faf9617c53607e583f6e6ff70a4ac9522d490faf Creating a new wineprefix just for Firefox isn't really necessary. You could remove the global override and set individual overrides for each Office app (Word is the only one that I know for certain needs it). Or you could leave the global override in place, but add an override for Firefox only setting usp10.dll back to (builtin, native). If Firefox is the only other app you have installed in that wineprefix, and you don't plan on installing any others, the latter is probably the easiest way to handle it.
