Firefox is my default browser. Many web pages try to send Email through the default browser; one example is WeatherBug when you click on feedback. When I do that (on Chrome, incidentally), an infinite loop seems to be created with mailto because I don't have Firefox set up to send Email (and don't particularly want to do so). When this occurs, I have to quit or sometimes force quit and reopen Firefox. It would not bother me if a single tab were created with an error message, but many, many tabs are created in that infinite loop. I suspect that this is a bug in the way Firefox processes such mailto requests.