Steps to reproduce: Screen capture- https://testing-1.tinytake.com/sf/MjM3NTEzM183MjI3Nzg2 1. Open the latest nightly 2. Go to about:config 3. Open a new window(Menu-> New Window) 4. On the new window, go to about:config 5. Observe the second window Actual result: The new window exists Expected result: New window should open about:config Note- this is also reproducible with newtab and all urls that start with "about:" as well. The regression range is: Last good revision: 3f96ca5e9d2deeaa6206313c981fa32d46062725 First bad revision: 6cfa628374192bc053d5837c892fc5d6f44a6778 Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=3f96ca5e9d2deeaa6206313c981fa32d46062725&tochange=6cfa628374192bc053d5837c892fc5d6f44a6778 Looks like the following bug has the changes which introduced the regression: https://bugzilla.mozilla.org/show_bug.cgi?id=1433938

This happens because the first result is now a switch-to-tab result, and when you choose a switch-to-tab result and the current tab is "blank," we close the current tab as a convenience. In this case there's only one tab in your new window, so the whole window closes. It doesn't have to be an about: page, could be anything that triggers switch to tab as the first result. Just to make sure before we close this bug, could you please confirm that that's what you're seeing?

Yes, that is what I see. If that is intended, we can close it.

Thanks for confirming. I'll mark this invalid since it's not a bug.