About 20% of all Firefox surfers that have visited www.jangaron.net during the last month already used Firefox 3 -- and couldn't start the game! After a really small patch, Jangaron 0.52 now works completely in Firefox 3.
My workmate Jan found a bug in the browser abstraction code: To let standard-compatible browsers simulate IE behavior (yes, I know, it should be the other way round!), I checked whether MouseEvent is defined. Since MouseEvent is supposed to be a constructor function, I used typeof MouseEvent=="function". For reasons beyond my imagination, Firefox 3 changes the type of MouseEvent to "object", so the check failed. Now, I simply use typeof MouseEvent!="undefined".
After quick-fixing the bug (no new version number, just reload / maybe clear browser cache), the full game now works in Firefox 3. However... it runs unbearably slow :-(. I started searching for similar problems and found many disappointed Firefox users who reported that version 3 is actually quite slower than 2 (at least in certain circumstances).
Currently, there is not much more I can, or better am willing to do about it. Maybe the guys over at Mozilla will come up with some performance tips or patches soon. Until then, I do not recommend using Firefox 3 to play Jangaron. If you are brave and try, I would really be interested in your experience. By the way, I didn't yet bother to patch the "stable version" 0.43, which has the same bug, so please use 0.52 with Firefox 3.
One last hint, if you want to use Firefox 3 for surfing and Firefox 2 to play Jangaron: just google for "firefox.2 firefox.3 parallel". Essentially, you create a separate profile for each Firefox version so the other one does not mess it up, and start the program with command line switches that tell it a) to use a certain profile and b) not to reuse the running Firefox instance.
After being a bit disappointed by Firefox 3, Opera 9.5 and Internet Explorer 8 are my next candidates...