User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

1. Set xpinstall.signatures.required to false in about:config
2. Set extensions.allowPrivateBrowsingByDefault to true in about:config
3. Try to install https://github.com/rufketo/isAllowedIncognitoAccess_demo/releases/tag/v1.0
4. Go to about:debugging#/runtime/this-firefox, try to load the downloaded extension as "temporary add-on".
5. Set extensions.allowPrivateBrowsingByDefault to false in about:config
6. Try to install https://github.com/rufketo/isAllowedIncognitoAccess_demo/releases/tag/v1.0
7. Set extensions.allowPrivateBrowsingByDefault to true in about:config
8. Restart the browser and open about:addons

Actual results:

Step 3: Message is displayed that the add-on cannot be installed and is corrupted.
Step 4: Error details: manifest.incognito set to "not_allowed" is currently unvailable for use.
Step 6: Installation works.
Step 8: The extension's icon is missing in the toolbar while it is activated in about:addons.

See also https://github.com/rufketo/isAllowedIncognitoAccess_demo/blob/main/findings.md (top-level if branch).

extensions.allowPrivateBrowsingByDefault is true by default in Tor Browser.

Expected results:

Step 3: It should be possible to install the add-on.
Step 8: The extension should remain functional.

Related: https://bugzilla.mozilla.org/show_bug.cgi?id=1678841

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Hello,

I’ve managed to reproduce the issue on the latest Nightly (85.0a1/20201123095316), Beta Developer Edition (84.0b4/20201122152513) and Unbranded Release (83.0/20201112153044) under Windows 10 Pro and Ubuntu 16.04 LTS.

The results documented in the “Actual results” section are the ones I’ve also obtained, with a slight exception to the Step 8 actual results. To be more precise, after restarting the browser, the add-on icon is still present on the toolbar and functions as it should. However, disabling and re-enabling the extension from about:addons causes the icon to disappear, even though the add-on is enabled, as mentioned in the Step 8 actual results.

This preference is going to be removed in bug 1661517.

The severity field is not set for this bug.
:mixedpuppy, could you have a look please?

For more information, please visit auto_nag documentation.

Setting allowPrivateBrowsingByDefault is not a supported feature. It will be removed as mentioned.