530. Briefly: Adding a new entry to Default applications in Gnome 3. Example using Firefox

I'm tired of google chrome/chromium -- for some reason more and more websites are rendering incorrectly in it. Part of the reason is because I refuse to allow just any website to set cookies, but that can't explain all instances (e.g. I'm having major issues with any elsevier journals). I'm also tired of google in general, especially after having spent some time with google plus.
Anyway, I recently showed how to install firefox: http://verahill.blogspot.com.au/2013/11/528-briefly-setting-up-64-bit-pre-built.html

I'll show here to set it as a selectable application in the System Settings/Details

At the beginning the following selections are available:

The key to adding a new 'Default Application' is simply making sure that it appears in the MIME file type associations. And one way to do that is to create a .desktop file and use update-desktop-database to read it:

sudo cp /usr/share/applications/iceweasel.desktop /usr/share/applications/firefox.desktop
sudo sed -i 's/Iceweasel/Firefox/g' /usr/share/applications/firefox.desktop
sudo sed -i 's/Exec=iceweasel/Exec=firefox25/g' /usr/share/applications/firefox.desktop
sudo sed -i 's/Icon=iceweasel/Icon=firefox/g' /usr/share/applications/firefox.desktop
sudo update-desktop-database

Once that's done we get the following:

 You can then set up a shortcut launcher, e.g.

(you could of course just have it execute the command directly, but what's the challenge in that?)