I'd like to repost the question asked at this link: https://support.mozilla.org/en-US/questions/710217?fpa=1 as it doesn't seem to be active any more. To the reply "No you cannot because Firefox is not a email client." I have a response which is this: I think you may be wrong or there may be a trick to get around this issue because I have another (very lucky) issue. I have removed the default email client as I wanted to use firefox for mailto links. When I now click a mailto link I get a "mail client not found" error and then for some (lucky) reason execution is passed on to firefox. Firefox's mailto action is set to "Use Gmail" and so it does, the result being a standard Gmail compose message window. The only problems are that I get the error first and secondly the email address in the composed message is the address I clicked on directly followed by "FirefoxHTML\Shell\Open\Command". I hope to fix both these problems and this is where I need help. Since I uninstalled the email client which seems not to have uninstalled correctly... (you'll never guess which it is!) when I run Default Programs|Set Associations, the mailto protocol is no longer listed. It wouldn't have helped if it was though because the only browser listed was Chrome. What I'm hoping to do is edit the mailto entry manually (maybe in the registry?)