Comment 45 for bug 107261

The problem isn't limited to Firefox only, nor to applications that use pango (like Firefox and Abiword do). E.g. Opera, which I believe doesn't use pango, exibits the same behaviour. It's due to some complex interaction between the used font and application, so with some unlucky combinations of font and software it is much more pronounced. Ironically, the otherwise very high quality Microsoft Core Web Fonts deliver here some of the ugliest displays. I mean specifically the somewhat dated versions of these fonts from msttcorefonts, which are the only ones that are freely redistributable. When I replaced this version of Arial with that from Windows XP, the results were much better.

This was described in detail here:
http://lists.kde.org/?l=koffice-devel&m=115609793729861&w=2

By now, I use Konqueror on the sites that display Hebrew or Arabic vowels.