Tonight, FireFox (current version) removed a number of the extensions I had installed, including yours. The message says the security of the extension has not been verified.
If I try to reinstall any of the removed extensions, that is blocked (but giving a misleading error message saying "check your connection" - which isn't the reason - FF blocks this).
Hope you can get it verified and going again soon!

I'm currently unable to install any add-on from AMO. So it seems like there is a problem on AMO which might be related to your problem.
What is AMO?
-- Larry
===== Orig. Msg. =====
From: Robbendebiene notifications@github.com
Date: Saturday, May 4, 2019 (1:50 AM)
To: Robbendebiene/Gesturefy Gesturefy@noreply.github.com
cc: larryedwards larryedwards@gci.net, Author
author@noreply.github.com
Subj: [Robbendebiene/Gesturefy] FireFox auto-removed the Gesturefy extension (#395)
I'm currently unable to install any add-on from AMO. So it seems like there is a problem on AMO which might be related to your problem.
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[ { "@context": "http://schema.org", "@type": "EmailMessage", "potentialAction": { "@type": "ViewAction", "target": "https://github.com/Robbendebiene/Gesturefy/issues/395#issuecomment-489312450", "url": "https://github.com/Robbendebiene/Gesturefy/issues/395#issuecomment-489312450", "name": "View Issue" }, "description": "View this Issue on GitHub", "publisher": { "@type": "Organization", "name": "GitHub", "url": "https://github.com" } } ]
AMO = Mozilla Add-ons = https://addons.mozilla.org
This issue is due to expiration of Mozilla's signing cert.
See https://bugzilla.mozilla.org/show_bug.cgi?id=1548973.
You can already install a Hotfix for this. For more information checkout here: https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/
Thanks, Robin.
About:Studies says the hotfix is installed, but none of the subject
extensions have been reactivated. So it seems Moz still has work to do
on the fix. (BTW, this is on a PC running Windows.)
-- Larry
===== Orig. Msg. =====
From: Robbendebiene notifications@github.com
Date: Saturday, May 4, 2019 (10:07 AM)
To: Robbendebiene/Gesturefy Gesturefy@noreply.github.com
cc: larryedwards larryedwards@gci.net, Author
author@noreply.github.com
Subj: [Robbendebiene/Gesturefy] FireFox auto-removed the Gesturefy extension (#395)
You can already install a Hotfix for this. For more information checkout here: https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/
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[ { "@context": "http://schema.org", "@type": "EmailMessage", "potentialAction": { "@type": "ViewAction", "target": "https://github.com/Robbendebiene/Gesturefy/issues/395#issuecomment-489350682", "url": "https://github.com/Robbendebiene/Gesturefy/issues/395#issuecomment-489350682", "name": "View Issue" }, "description": "View this Issue on GitHub", "publisher": { "@type": "Organization", "name": "GitHub", "url": "https://github.com" } } ]
I'm closing this since Mozilla released an update which fixes the problem.
Most helpful comment
This issue is due to expiration of Mozilla's signing cert.
See https://bugzilla.mozilla.org/show_bug.cgi?id=1548973.