Hello everyone!
I have been using this ant video downloader and player for sometime in windows and macs. which downloads video I like and converts them to mp4.
When I stared figuring out which version of Linux my systems played well with. Than I decided mint Linux played better now I am using it on two systems. This one is a IBM T500. I had issues with installing the converter for this addon and I decided to contact the creator.
They told me that the auto install of the converter has issues in Linux Mint debian systems seem to be able to install plugins or addons better than RPM based distributions why I have no clue. I was asked me to download FFmpeg stand-lone from internet. Which did not work still would not stop downloading webm video extension which did not convert to mp4. After a few email tickets back and fourth. Here is the solution which works in Linux Mint 18 and might in other Debian systems.
Install ant video downloader by search for it in the Firefox addons
To fix the Firefox issue of not downloading webm video. Open firefox type in url field
answer the warranty question than Type in the search
Disable each one of the webm list than restart Firefox than go to ant video download click preferences click install converter. after it installs try downloading a video from youtube. Which now should be converted to mp4. Thought I would share this with all.