[Affected versions]: - Firefox 56.0 beta 8 - Nightly 57.0a1 - for Sync section [Affected platforms]: - Win 7 32-bit - Ubuntu 16.04 32-bit - Mac OS X 10.9.5 [Steps to reproduce]: 1. Open a new tab and select FoxHead icon to start the tour 2. Click on Add-ons section and then "Show Add-ons in Menu" button 3. Menu Panel opens with Add-ons icon highlighted - Click on the icon 4. Return to tour and go to Sync section 5. Enter an e-mail address and click Next [Expected result]: 3. about:addons is opened in a new tab and the user can continue the tour 5. Create Account opens in a new tab [Actual result]: 3. about:addons opens in the same tab. Back button is disabled. 5. Create Account opens in the same tab. Back button is disabled. [Regression range]: - Not a regression, it also reproduces on Nightly 56.0a1 2017-06-20.

its by design, Wont fix

(In reply to Francis Lee [:frlee] from comment #1) > its by design, Wont fix I understand that the following behaviour is expected: click the "Show Add-ons in Menu" button -> about:addons opens in the same tab. What is unclear is the fact that in a private window the behaviour is different: about:addons opens in a new tab. Is this expected, too or a new bug must be filled?

the rationale is described in bug 1374544