What happened to TableTools2? Can we get it back?

I used to use the TableTools2 addon in Firefox on a daily basis. It suddenly disappeared a couple months ago. Can someone check on why it disappeared and how to get it back?

http://addons.mozilla.org/en-US/firefox/addon/tabletools2/

Found out this was due to an update that enforced the extension signing requirement. Other than hacking the Firefox configs, how does this get fixed?

TableTools2 was a XUL-based (legacy) extension which was not compatible with Firefox Quantum (versions 57+). At some point, those were removed from the Add-ons site. There might be other places to download it, but it won’t be useful in recent versions of Firefox without a major rewrite.