I doubt IE counts, but do you think you could maybe move/rename the files to force a cache/cookie update on everyone? That way, users who don't login often will not keep asking every few hour why OmnomIRC is broken because they forgot to clear their cache.
Also after cache/cookie clearing, it's confirmed to work in FF and Chrome. In Opera it already worked.
However, in Firefox the space between text lines is too large, causing some text to be hidden and a vertical scrollbar to appear.
