I, too, have been having great difficulty with this. Thanks to the help here I have persevered.

This is what does it for me with Mozilla Browser

Install MPlayer – it didn’t work until I did.
Prior to selecting the video make sure that the Plug-ins Browser Default and Shockwave Flash are disabled
Select Video
Tap Preferences in top RH corner, select Standard Quality and RealPlayer
Tap OK to save
Tap Launch in Stand Alone Player
Comments: The disabling of the Plug-ins and the selection of Quality and Real Player settings may need to be checked each time you come to play a video. It seems to me that they can slip. In fact you may want to re-enable the plug-ins anyway after finishing with the videos.

I hope this is of help to someone.