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. Install https://github.com/rufketo/isAllowedIncognitoAccess_demo/releases/tag/v1.0-incognito_allowed

3. Set extensions.allowPrivateBrowsingByDefault to false in about:config
   4.1. Open and reload the add-on's settings in about:addons
   4.2. Change the "Run in Private Windows" to "Allow".
   4.3. Click on the extension's icon.

4. Set extensions.allowPrivateBrowsingByDefault to true in about:config.
   6.1. Open and reload the add-on's settings in about:addons
   6.2. Click on the extension's icon.

5. Set extensions.allowPrivateBrowsingByDefault to false in about:config
   8.1. Open and reload the add-on's settings in about:addons
   8.2. Change the "Run in Private Windows" to "Don't Allow".
   8.3. Click on the extension's icon.

6. Set extensions.allowPrivateBrowsingByDefault to true in about:config.
   10.1. Open and reload the add-on's settings in about:addons
   10.2. Click on the extension's icon.

Actual results:

Step 4.1 and 8.1: Option "Run in Private Window" is displayed.
Step 6.1 and 10.1: No option "Run in Private Window" is displayed.

Step 4.3 and 6.2: extension.isAllowedIncognitoAccess(): true is shown.
Step 8.3 and 10.2: extension.isAllowedIncognitoAccess(): false is shown.

I.e. when extensions.allowPrivateBrowsingByDefault is true then the option "Run in Private Windows" is not visible, while extension.isAllowedIncognitoAccess() can still be either true or false.

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

extensions.allowPrivateBrowsingByDefault is true is the default in Tor Browser.

Expected results:

Step 6.1 and 10.1: Option "Run in Private Window" is displayed and affects the result of extension.isAllowedIncognitoAccess().

I.e. extensions.allowPrivateBrowsingByDefault should not affect if the option is displayed.

Related:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1678847
• https://bugzilla.mozilla.org/show_bug.cgi?id=1538546
• https://bugzilla.mozilla.org/show_bug.cgi?id=1557792
• https://bugzilla.mozilla.org/show_bug.cgi?id=1558075
• https://bugzilla.mozilla.org/show_bug.cgi?id=1536459

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 (85.0a1/20201122213806), Beta (84.0b4/20201122152513) and Release (83.0/20201112153044) under Windows 10 Pro and Ubuntu 16.04 LTS.

Using the provided extensions, the results I’ve observed match the ones originally reported.

This pref 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.

Use of allowPrivateBrowsingByDefault is not supported, it was used at the time as a feature fallback. Edge cases and issues have probably developed since as we don't work on supporting it being set to true. 1661517 will remove the setting.