… In this second year of Test Pilot, we’re making a concerted effort to make our work even more public by sharing all of the user research we conduct on our experiments. …
On the down side: the experiment in which I was most active ended prematurely. The unexpected loss of functionality was a very ugly user experience, which probably can not be measured by Test Pilot …
In retrospect, I might have regained functionality by copying the relevant file – I guess, ~/Desktop/Old Firefox Data/…/extensions/tabcentertest1@mozilla.com.xpi …
… instead, I took the opportunity to seek an alternative. I chose one that’s compatible with my extensions, not compatible with WebExtensions.
FWIW the testpilot programme appears to have closed down permanently some time ago. It’s unclear to me if the software used for it is Open Source or reusable by other projects.