Steps to reproduce: - Open Nightly with a fresh profile. I've only verified on OSX 10.12.6 so far with 63.0a1 (2018-08-23) (64-bit). - Go to about:preferences and turn off "Open links in tabs instead of new windows" - Click a link in another app (from email in Mail.app as an example) - See empty new browser window (as if New Window was selected) instead of loaded page for link. It is not URL specific. I ran mozregression, and it pinpointed the following pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=3d50f935615c9ba9179e8ab0dbb244ca65626967&tochange=486f7f825c6bfb4b31cb76c49174f2880dd8af19 Turning on "Open links in tabs instead of new windows" causes the sames links to open and load content in new tabs. This is the only setting change required to cause the incorrect behavior.

I think this could be a possible dupe of Bug 1485577 but easier to test on linux.