I had the situation the other day where by every time I got saw a mailto link in Firefox or Mozilla and clicked on it. Evolution would launch. The problem is I use Thunderbird for my email needs.
So how do you change the default email application in Firefox/Mozilla?
Open Firefox and type about:config into the location bar and press enter
Type in `mail' in the filter: field and one of the entries you will see is a preference named: network.protocol-handler.external.mailto and it's value should be true
Now that we have confirmed firefox is setup to send it's mailto requests to an external source. How to we find out what application it's supposed to launch
To find out which file moz/ff queries when it launches a mailto link I had to use strace
echo `pwd` >> /etc/ld.so.conf && ldconfig -v
cd /path/to/firefox/ && ./firefox-bin