[arch-dev-public] dropping version from libdir in firefox and thunderbird

Hi, both apps generates a .desktop file that contains the Exec option from /usr/lib/app/$pkgver and every time we update we must set up the default browser/email. Since new versions are released every 6 week, it started to be annoying and with version 8, we are dropping the version. Be sure your extensions are installed in the right directory. -- Ionuț