Thanks for making that a sticky topic! I'm having trouble adding media since upgrading to WP 2.8 I've tried the list of suggestions to no avail.
Essentially when I click the media buttons, nothing happens. I can right click & open the link in a new window, and upload media that way, but it won't insert the code into the post so I have to go to the media link, copy the url, and write out my caption code manually. Doable, but discouraging.
I'm in a current Firefox 3.0.11 with a fairly typical set of plugins (including Flash of course, which I just reinstalled in hopes of fixing this) as well as web developer toolbar & greasemonkey, which only has a script to block third party iframes, but I disabled it anyway to see if it'd help & that's a no go.
I have a couple of wordpress plugins and can disable those as well if needed, but I thought I'd check here first... Anyone else seeing an issue like this?