Bug 1433324 made activity stream the only default page for about:home and about:newtab and bug 1438367 made them load the same way, potentially only about:home (to match up with the official Firefox Home (?)) would be needed. I suppose about:newtab would just become an invalid url if someone were to try to open it directly? This probably requires fixing up a bunch of tests / references: https://searchfox.org/mozilla-central/search?q=about%3Anewtab There's also preloading of new tabs, which would need to preload about:home instead, which seems to match up with the _isPreloadingEnabled check to not preload customized new tabs anyway: https://searchfox.org/mozilla-central/rev/ce9ff94ffed34dc17ec0bfa406156d489eaa8ee1/browser/base/content/tabbrowser.js#1766-1773 about:preferences does allow for setting new windows to be blank separately from new tabs to be blank, so that logic will probably need to change.