Security researcher Jordi Chancel reported two issues involving addressbar spoofing. The first of these is a "high" rated security issue on on Firefox for Android involving the scrollTo() method to scroll a page. In this attack, scrollTo() is used to scroll the addressbar out of view while replacing it with a fake addressbar created by the attacker when a new tab is opened.
The second flaw is a "low" rated security issue affecting Desktop Firefox. In this attack, when a URL which is invalid for an internal protocol is pasted into the addressbar, the addressbar contents may be manipulated to show the location of an arbitrary website instead of the one currently loaded. This issue is mitigated by the protocol being prepended to the displayed URL, making the address less likely to be confused with the appended URL.
Both of these attacks can lead to potential spoofing by a malicious site.