Update Regarding Add-Ons in Firefox
Firefox users can check if they have Studies enabled by going to:
Firefox Options/Preferences – Privacy Security – Allow Firefox to install and run studies (scroll down to find the setting)
Studies can be disabled again after the add-ons have been re-enabled
It may take up to six hours for the Study to be applied to Firefox. Updates:
Clarified that the Studies fix applies only to Desktop users of Firefox distributed by Mozilla. (May 4, 12:03 EST)
We’re aware that some users are reporting that their extensions remain disabled with both studies active.
Source: blog.mozilla.org