Bug 362549 fixed this for Firefox, but not for us. philor's solid STR to trigger this: 1. Cmd-click http://example.com:443/ (which will conveniently time out after a while). 2. Focus the new tab, it should be white. 3. Focus any tab with content. 4. Focus the tab loading example.com, it should still be white, but now will show the content of the tab from step 3. I wonder if maybe this is / is related to bug 313811 (which was never backed out on the trunk)?

maybe. Why don't you try your suggestion in https://bugzilla.mozilla.org/show_bug.cgi?id=313811#c39 locally to see if it fixes it?

I finally was able to back that part of bug 313811 out in a way which didn't throw exceptions and prevent window opening, and it didn't help this (or bug 401328).

Duping over to 401328, since it's definitely the same issue.