hi tom, this is/was caused by an unforeseen technical problem unfortunately (an expired certificate used in the process of verifying addon signatures).

a fix for this is already being rolled out - for details, please see: https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/

@philipp Thanks! It is really annoying though. When will it be fixed?

Hi TomSmithNP, by default, Firefox checks for new studies every six hours. However, please check your settings on the Options/Preferences page as follows:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

In the search box at the top of the page, type stud and Firefox should filter to the "Firefox Data Collection and Use" section. Here, make sure you have a check in the box for "Allow Firefox to install and run studies". If you prefer to turn it back off after the patch comes through, that's fine.

More info in this new support article: Add-ons disabled or fail to install on Firefox

TomSmithNP said

@philipp Thanks! It is really annoying though. When will it be fixed?

You should have received the Firefox 66.0.4 update by now but, if not, see Update Firefox to the latest release.