- Replaced all threes with twos...
    More precisely, the add-on now listens to two finger gestures,
    which are easier to produce in my opinion
- Reversed left/right tab swipe default behavior.
    This is more intuitive since most modern touch interfaces
    interpret movements in this reversed way.
- Changed compatibility settings to the current firefox versions
- Unfortunately I had to remove all Japanese strings for now,
    because I can't read them.
- Added some information about Three/Two Finger Swipe to
    the bootstrap.js and LICENSE.txt