Bug 1894688

Description of problem: 
Violentmonkey is a userscript manager add-on. After updating Firefox (RPM version) to 82.0.2, all my userscripts from Violentmonkey were deleted. I tried to import them from a .zip backup and got this error on console: "Error: Could not establish connection. Receiving end does not exist.". I also tried to install a new userscript, it didn't work.

This does not happen on Windows or on previous versions of Firefox (RPM).

Version-Release number of selected component (if applicable):
Firefox 82.0.2 on Fedora 32 (it seems Fedora 33 is also afected)

How reproducible:
Always

Steps to Reproduce:
I suppose you could try any of these scenarios:
- Scenario A: On Firefox 82.0.2, install a new userscript. Example: https://greasyfork.org/en/scripts/393967-resize-image-on-open-image-in-new-tab
- Scenario B: On Firefox 82.0.1, add some scripts to Violentmonkey and then update to 82.0.2.
- Scenario C: On Firefox 82.0.2, try to import a Violentmonkey usercript backup.

Actual results:
- Scenario A: After clicking the "Install script", button, an empty page is displayed.
- Scenario B: All userscripts are deleted.
- Scenario C: Userscript backup import fails with "Error: Could not establish connection. Receiving end does not exist."

Expected results:
- Scenario A: After clicking the "Install script", button, a moz-extension:// Violentmonkey page is displayed to install the script.
- Scenario B: All userscripts are preserved.
- Scenario C: Userscript backup is imported.

Additional info:
More people affected:
- https://old.reddit.com/r/firefox/comments/jmf3kn/after_the_latest_update_fedora_33_firefox_now/
- https://old.reddit.com/r/firefox/comments/jlqud1/userscripts_wiped_after_upgrading_to_ff82/

Given the nature of the bug, I think it might related to how Firefox handles add-on data storage. I'm not sure if it's specific to Fedora or Linux in general.

Sorry if I did not report this bug correctly.