Is it possible to install a previous version of Thunderbird? Thunderbird 60 breaks several important add-ons, thus I would stick with a previous version preferably the last working one, however I cannot find a way to install.
That depends on whether or not you have a copy of an older Thunderbird somewhere.
Keep in mind that it is no longer supported, as well, so you are running Security risks if you do that.
Looks to me like all that’s needed is to enable the Mozilla repo and get YaST or Zypper to install it:
http://download.opensuse.org/repositories/mozilla/openSUSE_Tumbleweed/x86_64/MozillaThunderbird-52.9.1-1.44.x86_64.rpm
Install tumbleweed-cli, and read the stuff in
sudo tumbleweed --help
It allows you to move back and forward between tumbleweed snapshots. Mind, this is different from the btrfs snapshots. It would at least make sure the rest of the system is consistent with the installed firefox.