I'm using NoScript 2.4.8, on Firefox 14.0.1, on Linux Mint, and on a fresh installation of Joomla 2.5, when I click the 'Add Image' button on the TinyMCE toolbar on the backend, I get a notification that says:
Quite annoying, as nothing is to be found on Google on this matter, and I have already Allowed (whitelisted) the website in NoScript. I had to manually enable and disable various add-ons before I found out that it was NoScript that was responsible for this.Sorry, but we have noticed that your popup-blocker has disabled a window that provides application functionality. You will need to disable popup blocking on this site in order to fully utilize this tool.
Looking at the NoScript Options, I didn't notice any relevant option that could be responsible, so I post it here as a possible issue... I'll try to post this to Joomla and TinyMCE forums as well.