This has been happening to me for several weeks now and didn't know if it was someting to do with my machine or not. I still don't but was hoping that it would disappear after yesterday's 2.01 upgrade, no luck.
My machine is not bogged down in the least and I can go to any of my other FF tabs with no problem but quite often, after selecting the PUBLISH button, I am stuck waiting for this one process to finish i.e. the FF tab takes up to a minute to finish the progress bar showing that it has completed whatever it was doing. Note, I can use the other open tabs to surf with no problem and they do return pages with no problem (hence I don't thnk it is FF) and I can pretty much immediately go to my own blog and see the results that I am waiting for the PUBLISHing tab to finish.
Yes I updated FF yesterday to 1.501 but as I said, this has been going on for weeks although not with every post, it may even be just on the posts that I am making several edits to before actually PUBLISHing.
Finally, I lost all my data yesterday so I started with a brand new WP download, install, DB so that alleviates a corrupted DB on my end. Any ideas? TIA.