The recent versions of Extensions at addons.mozilla.org should be signed.

https://addons.mozilla.org/firefox/addon/fireftp/ 2.0.26 Released November 27, Works with Firefox 32.0 - 44.*

https://addons.mozilla.org/firefox/addon/adblock-lite-firefox/versions/ Version 0.2.9 Released December 14, 2015 951.7 kB Works with Firefox 38.0a1 and later

https://addons.mozilla.org/firefox/addon/awesome-screenshot-capture-/ https://addons.mozilla.org/firefox/addon/awesome-screenshot-capture-/versions/ 2.4.11 Works with Firefox 26.0 - 43.*

https://addons.mozilla.org/firefox/addon/xmarks-sync/ Version 4.3.7.1-signed Works with Firefox 3.0 - 43.*

So check for updates as chances are you are one or more Extension updates behind. Also you appear to have downgraded to 41.0.2 and not 42.0

read that Xmarks may have been acquired by LastPass https://blog.lastpass.com/2015/12/easily-enable-lastpass-in-firefox-43.html/

Thanks for the reply James Xmarks was acquired by Lastpass, but it is a poor substitute, so I stick with Xmarks for keeping track of bookmarks between differing machines. The machine I posted the question on was on FF 41.2. I could not find a FF42 to shift back to. so took the next best thing This one is on FF42. It was primarily on this machine I had the most problems. I upgraded and all my apps were wiped, most frustratingly my Fire FTP which had several user logins and addresses I use for work. I had not saved those but luckily was able to roll back my machine and get them back. I am aware I can overwrite the need for signed apps in the config screen, but in what way is the "upgrade" an upgrade if I have to do that to get functionality back ? Frankly Firefox, which I have used since it's inception has been nothing but hassle for the last year or so. I hit freezes and problems I do not see with other browsers. This is not just on one machine, this on several machines. We seem to be hitting the same sort of problem that Apple and Microsoft hit - a very bright techy in a room releases updates frequently but never tests them properly at grass roots level, so they cause more problems than they solve.

If anyone has access to that tech - give him a nudge get him to fix what he has broken, or if he MUST have signed apps, let the developers of those apps know and be able to comply before making changes .....

Sorry, it isn't a matter of Mozilla not testing Firefox properly with regards to "signing" of extensions, but of Mozilla changing the standards that ALL extensions developers need to follow. The "signing" of extensions was announced all the way back in Feb 2015 via a Mozilla Add-on blog that "extensions developers" should be following, and possibly via a "mailing list". And the "enforcement" version was pushed-back three versions - so it shouldn't have come as a surprise in Firefox 43. There were "warning" messages showing in the Add-ons Manager since Firefox 40 for each extension that wasn't "verified" with a note of "caution". And a link to this - https://support.mozilla.org/en-US/kb/add-on-signing-in-firefox - in Firefox 42 at least, if not an earlier version.

Bottom line is that Mozilla created Firefox which add-on developer "extends" via their extensions. So when Mozilla changes the parameters for extensions that may be installed in Firefox, the add-on / extension developers have to change / update their add-ons.