How to have 'mailto' (clicking addresses) open a new email in Gnus?

[Marius Hofert]

Sometimes, email addresses on websites are links, which, when clicked, open a 
new email (with corresponding address) in the default email program. I figured 
out that Firefox has a setting (Preferences -> Applications -> mailto) but how 
can I set it to open a new email in Gnus?

I found some solutions, but they seem pretty old and not so easy to understand:

https://groups.google.com/forum/#!searchin/gnu.emacs.gnus/mailto$20firefox/gnu.emacs.gnus/DaJTxALQoDw/N_xm3Uoe86kJ[1-25]
http://article.gmane.org/gmane.emacs.help/49827

Is there any easier way? (Emacs 24; Ubuntu 12.04; Firefox 14.0.1; Gnus 5.13)

Cheers,

Marius