Anyone????

I assume you saw that on a site you use to read/compose emails. I would definitely only trust it on your own email site. "mailto" is a protocol used for email links, like: mailto:bob@example.com Firefox doesn't know how to send links like that to your email site unless it's Gmail or Yahoo mail. All others need to be set up, and it's super-helpful if the email website offers you a way to do that instead of having to guess/experiment. More info on Firefox's handling of mailto in this article: [[Change the program used to open email links]].