I was under the impression Webextensions were still experimental in Firefox See for example

• Mozilla Add-ons Blog: Add-ons in 2017
  https://blog.mozilla.org/addons/2016/11/23/add-ons-in-2017/
• https://blog.mozilla.org/addons/category/web-extensions/

When Webextensions add-ons are available for Firefox they will be signed by Mozilla. Have you any indication that the Webextensions Evernote and Pushbullet that you mention have been signed by Mozilla and are ready for use on Firefox other than for testing purposes.

Well, they're both on addons.mozilla.org and not marked "special" in any way that I'm aware of:

• https://addons.mozilla.org/en-US/firefox/addon/pushbullet/
• https://addons.mozilla.org/en-US/firefox/addon/evernote-web-clipper/

I'm sorry to not know more, but is there a way for me to check whether they're signed by Mozilla?

You could try the previous version of these Extensions.

https://addons.mozilla.org/firefox/addon/pushbullet/versions/ https://addons.mozilla.org/firefox/addon/evernote-web-clipper/versions/

OK so you are using add-ons hosted by Mozilla, and those are both now Webextension types as you say. Such hosted extensions that are normally visible are signed. In addition to trying the earlier versions as suggested by James I note that they both have support and home sites maybe they will have information about problems and solutions.

Additionally

1. You can post in Mozilla's own add-ons support site see if you can get any news over there:
   • https://discourse.mozilla-community.org/c/add-ons/add-on-support
2. Note on the Mozilla Download pages you may add a review for add-ons that you have downloaded, you should add a review stating what problems you found.

@james: yes, I've reverted to earlier (working, non-Web Extension) versions

@john99: thanks for the support pointer!

So, basically, developers are being pushed towards Web Extensions, but the platform isn't quite ready it appears.