Disabling 'onClick' in FireFox 35

I've added a video to my site using the default html5 video player. The code is like this.

<video width="100%" height="100%" controls>
  <source src="http://ift.tt/16vTSab" type="video/mp4">
</video>

I wanted to make it so a click on the video stops or starts the video. So I added this:

onclick="this.paused?this.play():this.pause();"

And all good. Until Firefox 35 adds this very function to the player. So now you can only play the video by right clicking and selecting play. Terrible. So I thought up a javascript function something like this:

function startstop() {
  if ( FirefoxVersionNumber > 34 ) {
  do nothing
  } else {
  start or stop video
  }
  }

The bit I'm stuck on is how to check the browser version? All the ones I tried returned that Firefox version number was 5... which I think comes from the Netscape part.