I wish there was an option to disable the spawning of the "you have been updated" tab. I never read it, and, worse, the tab which was active when I closed Firefox will no longer be active, forcing me to go through a couple of tabs to find it again, while reloading all the tabs which I click through while searching.
I hope it also works with the "last session" tabs and doesn't pop up a homepage (If browser.startup.homepage_override.mstone is set to “ignore”, the browser’s homepage will not be overridden after updates.).
I love Firefox's about:config page, it has so many options.
There's got to be an about:config entry that tells Firefox whether it's already displayed that tab, which, at worst, you could manually edit before starting. But, even if that were an acceptable solution, I couldn't find it with a quick search for "display", "update", or "tab", nor even find an up-to-date list of entries (I think that http://kb.mozillazine.org/About:config_entries is quite old).
EDIT: Actually, I know for sure that there's some preference that controls this, because I just updated and didn't see the new page; but I forget what it is. One suggestion I saw in https://superuser.com/a/1392487 was to change various addresses to non-existent pages; based on the names of their default values, `app.update.url.manual` might be a relevant one.
I think that's already there. I must have done it long back since I don't remember the last time I got it. Could be a flag if it's not an option in preferences.
It's really annoying.