Yes, it offers that option. I use it. You probably need to change an option. Write on Firefox "about:preferences#applications". Search for mailto and change the value to Gmail. It should be there. If you have issues, please email me: http://www.google.com/recaptcha/mailhide/d?k=01NKj2PDsRo1XUKZ73GiSunQ==&c=BxMyIylpuNw4tPzCYDJq3uu4JQ4xzutfY3wA2GYrSRg=