Workaround for wrong checked icon in subviews with a RTL locale

Backport to Firefox 29 of:
https://bugzilla.mozilla.org/show_bug.cgi?id=998481
Get rid of xul.css
Update known compatibility info
Remove a redundant import call
Don't wait until closing about:customizing for to update the widget
Update localizations from babelzilla; Added French (fr), Dutch (nl)

Credits for the new localizations to ArielFr and markh,
respectively.
RELEASE 0.7