Browse Server button not showing

Hi
I have integrated the php version of ckfinder with fckeditor and it worked beautifully but suddenly the 'browse server' button has stopped showing in the fckeditor 'insert image' dialog.
I checked the config, uploaded everything but still no button.
Then it started working again for a while, then it stopped again.
The apparent randomness is a puzzle and makes debugging frustrating so I was hoping someone might have a clue as to what might be causing this behaviour.
In particular, what scenario the 'browse server' button not to show.
Many thanks for your thoughts.
Notes:
I have only seen this behaviour in Firefox 3.0.5 but haven't tested extensively in IE.
FCKeditor is integrated into Pommo.