Type “about:config” in address bar

promise to be careful

scroll down to “browser.startup.homepage_override.buildID;20140314220517”. Right click on it and select “reset”.

scroll down one below to “browser.startup.homepage_override.mstone;28.0” and do the same thing.

Close then reopen Firefox. You’ll see 2 tabs appear the 1st time, but that should be it…

When you reset these strings, you will need to modify your preferences again within Firefox (such as your homepage).