Problem: Firefox (2.0.0.3; Mac OS 10.4.9) renders some fonts (Gentium, for example) such that italicized text overwrites the preceding character or two. The result can be an unintelligible mess (shown here in Gentium font):

Safari and IE (Mac) don’t have this problem.

Cause: Firefox seems to have difficulty in rendering TrueType fonts in italic.

Fix: Hunt down and remove any TrueType versions of the offending font in all four of the possible font folders (~/Library/Fonts, /Library/Fonts/, /Network/Library/Fonts/, and /System/Library/Fonts/ — see “Mac OS X: Font Locations and Their Purposes“). Re-install the “font suitcase” version of the font (i.e., drop the font suitcase into one of those four font folders). Restart Firefox.