KDE's startup notification for Firefox has been broken for a while,
it seems to work for the first use, but subsequently fails.
(the bouncing icon just keeps on bouncing until it times out)
So far, the "fix" for this has been to reduce the notification timeout
or to disable it altogether. Choices that are less than ideal.
Rumor has it that this will finally be working in Firefox 3.6,
but it is NOT yet fixed in the most recent beta (3.6b3).
I've never stopped looking for a solution to this annoyance,
and yesterday discovered a patch
for Firefox (some discussion here
that simply moves a chunk of code - and fixes the problem!
I had to rebuild Firefox with '--enable-startup-notification' to get this working.