Added support for font smoothing in Firefox 25 on Mac OS X

[MartinSeeler]

Even though this vendor prefix will be available earliest in Firefox 25+ and only on Mac OS X, it's not a big deal to include it now.

Related to issue #1591
Based on https://bugzilla.mozilla.org/show_bug.cgi?id=857142#c83

[tagliala]

can you please post a screenshot with the difference?

[MartinSeeler]

Unfortunately not. I don't have a Mac and the ones I know are on vacation...But I will see what I can do.
This addition was purely precautionary and based on the comments in the bugzilla comments, where it seems to work properly.

BTW: I've seen that you already using this in your fork and didn't notice any differences on OSX 10.7.5.
Is it possible that this will only affect OSX 10.6 und lower?
I've got this idea from comment #89, where it says:
+skip-if(!cocoaWidget||OSX==10.6||OSX==10.7)) != osx-font-smoothing.html osx-font-smoothing-ref.html

[winterbe]

This is taken from the current FF Nightly Build on Mac OSX 10.8.4.

Without Font-Smooting:

With Font-Smooting:

[MartinSeeler]

Thx for the shot!

In my opinion the compass and edit icons looks better than before. On the other side, the code icon is now a bit too thin?

[winterbe]

The icons look the same as in webkit browsers. Without Font Smoothing the icons in FFOX all look too thick and blurred.