ನಮಸ್ಕಾರ, i am not sure whether this problem was solved, but on my machine, Firefox used to render kannada pages in an unreadable format. all the ವತ್ತು ಅಕ್ಷರ used to be one next to the other making the page unreadable. after much searching, i found the solution. if anyone else is facing the same problem and if u are using windows xp, please go to Control Panel --> Regional and language options --> Languages (tab) --->click on "Install files for complex script and left to right support". u'll need to pop the windows xp CD in for the installation to continue. restart after installation is complete and the rendering should work fine.
i would like to add that there are still some problems with the Firefox rendering (like headings come out looking strange, but readable), but most of them are minor. Also, all these rendering issues in FX is not limited to kannada, but common to all indic languages. IMHO, we should put up this note on the wiki help page so that other people know about it.
ಮತ್ತೆ ಸಿಗೋಣ ಚೆರೋ p.s --> if this problem was fixed long ago or if its a non-issue, please ignore.