I have, well, had the same problem. I updated my firefox from 3.0.8 to 3.6, that when i couldn't download with realplayer anymore. What I'm suggesting is just roll back your FFox browser to a previous state till they fix the FFox/Realplayer problem. Dats what i did & now i'm back downloading. Hope this helps anyone

Have you installed the latest RealPlayer update as mentioned here, next to the "A" in the big red circle: http://real.custhelp.com/app/answers/detail/a_id/7303/p/3/c/2222/r_id/119487

I am facing the same problem... cant download any vids like i used to with my previous version of FF...