Yes, exactly. You don't have to change forever, just for uploading your avatar.

FINALLY!!!

I have tried everything, even reinstalled my Java,

then I remembered I already have internet explorer installed, so I didn't remove my Firefox, I just came here and log in with my old explorer and it worked,

thank you Bookwyrm.

So if anybody else having the same issues, the problem is in Firefox

And it's not working even from the other computer.
Upload button just doesn't work.

Now I will try to log in from the laptop with Ubuntu. If it still doesn't working , than it's a bug on Kunena.

Yes I can only choose from avatars from Forum gallery. And still can't upload new picture. I will not change firefox, I got used to it. maybe there must be some extension to add.

Right now, you have a picture of an eye where the iris is a clock.

My best suggestion in this kind of situation is to change browsers - I think someone in a very similar situation had good luck with Opera, after Firefox wouldn't play nice. You could also try Safari or Chrome.