just in case, try and cleanup your internet cache (FF and java plug-in)
also check that the jogl.jar is the first in the jar list of your applet
my 2c’
Lilian 
I tried doing that and lots of other things i could think of and it still wasnt working, and i was baffled…
I ended up fixing i after trying lots of different code paths, and realised it was because i was leaving my code path blank…
codebase=""
Which worked fine in IE, but FF didnt have a clue where to look, so i swapped it to codebase="./" and bam, works great in all browsers i have tried, well i lie it refused to work until i downloaded latest webstarts and gluegen files and that took some messing around before it all worked perfectly, but it does now! So thanks for all the helps guys!