I'm having this problem too (Ubuntu 10.04 / Firefox 3.6.8)
My suspicion is that it's caused by Firefox trying to save anything that you "open with' in the temp folder (as it does in Windows). In Ubuntu the user does not have write permissions to the temp folder (/tmp).
I thought this may be easy to fix but I have just scrolled through about:config and no mention of a temporary folder :(
I'm having this problem too (Ubuntu 10.04 / Firefox 3.6.8)
My suspicion is that it's caused by Firefox trying to save anything that you "open with' in the temp folder (as it does in Windows). In Ubuntu the user does not have write permissions to the temp folder (/tmp).
I thought this may be easy to fix but I have just scrolled through about:config and no mention of a temporary folder :(