I found that its a issue with Firefox 3.0.9

Yeap, this happend also to me - version 2.4.5
And it is quit annoying- I have FF 3.0.10...

For a FF fan, this is quite annoying - same thing is happening to the comment module.

Anyone has any idea what it can be done (besides using IE ? :-)

Can't vouch for version 2.4# but I can never remember it not working and it works fine with b2 3.1 using FF 3.0.10

Maybe try deleting and re-uploading the _quicktags.plugin.php

This is strage - now it works (and this was just before deleting the file you have mentiond) :D

I'll keep looking to see if it appears again and in what circumstances and I'll post here my findings.

It could be a JS loading issue... ie a server lag, whatever.
There's a lot of code driving that Admin section

This is an ancient bug. Several people have reported it since the 1.10.x series at least.

See [url=http://forums.b2evolution.net/viewtopic.php?t=13150&highlight=b2evocallbacks]this post[/url] for more info.