In your browser address (URL) bar, type:
Answer “yes” to “you will be careful”
In the filter bar on the screen type (or copy and paste):
This will bring up the specific entry. Double click on the line to change the value from “false” to “true”
Do the same as the above, in the filter bar, for:
network.protocol-handler.external.mailto, toggling it from “true” to “false“.
Go back to the browser address (URL) bar and copy and paste the string below. Be sure to change “veino.com” to your actual domain name and the label at the end similarly:
Hit return and a message line above the page should appear (like for pop-up blocking messages) in the browser asking if you want to add this application to your mail. Click on “yes”.
Go to Firefox Edit > Preferences > Applications (using Linux FF – for Windows it is under Tools > Options > Applications), and select your new Google Apps entry as your default mailto: handler.
Return to about:config in the address (URL) bar and reset the values for the two variables to their original default values by repeating what you did before, reversing the toggling of values.
Close and restart Firefox, log in to your Google apps account and then try clicking on a mailto: link on any other web page. You should get a compose mail window loading, using your Google apps account. Yay!
Previously, I’d figured out how to have it open a new window to compose your message – but I can’t figure it out right now. Will update this post, if I remember how I did that.