The site inside bracket is the one of the embedding page.
In plain English, "Temporarily allow every kind of object served from http://videos.mozilla.org when embedded in http://videos.mozilla.org".
Now that NoScript has been integrated back into Babelzilla's workflow, I'll probably change the label to something a bit more explicit, even if not as long as the above (like "Temporarily allow *@http://xyz.com on http://jkl.com").