Been using Clippings for several years now. Recently cam up with a way to share/update copies of it on 3 machines I use. If you use Dropbox, make a common folder between the machines you require it on and set this folder as the default clippings .clipbak data source. Any changes are made available across all machines!
The Mozilla team is rolling out a fix for Firefox which should resolve the certificate issue affecting all add-ons. See their Twitter feed for details: https://twitter.com/mozamo/status/1124627930301255680