I am using Android ICS OS.
I downloaded Firefox.
I also downloaded the flash plugin.
Now The Videos are playing but not the audio.
I checked out android system volumes also but it did not solve the problem.
help me out.
Those are Desktop Firefox answers. They do not apply to Firefox for Android.
First make sure you are using the most recent version of Flash from Adobe's site currently Flash Player 11.1.for Android 4.0 (126.96.36.199) http://helpx.adobe.com/flash-player/kb/archived-flash-player-versions.html#main_Archived_versions
When the video has focus the sound can be adjusted but if you tap outside the video or pan the screen the focus is removed from the video and adjusting the sound of Flash is prevented.
Android has several sound levels. The guaranteed way to change the sound level is to use the Android settings.