Recent versions of Flash player has stability and security issue with the Firefox real player down-loader plugin, that is the reason the Realplayer downloader plugin doesn’t work in the Firefox.
It is very to fix that issue, just follow below few steps to fix the Firefox realplayer downloader plugin issue in your browser. you need to edit mms.cfg file of the Flash player.
Step 1: Before start to fix the issue close your Firefox browser.
Step 2: If your using Windows 7 32-bit operating system, you will find the mms.cfg file in the following directory.
C:\windows\System32\Macromed\Flash
Step 3: Open mms.cfg file in the note-pad with administrator permission (note: right click on note-pad icon, now it shows list of options. Select run as administrator and now open mms.cfg file by going File->open select mms.cfg file from the directory)
Step 4: Now add
ProtectedMode=0
at the end (in the third line).
AutoUpdateDisable=0
SilentAutoUpdateEnable=1
ProtectedMode=0
You had successfully fixed the issue the Firefox realplayer downloader plugin, now go youtube and download all the videos you liked..