Create a custom sandboxed webapp in Firefox

Google, Facebook, Twitter and others depend on getting as much information about you as possible and therefore use your account information to track and profile you not only on their services but also on 3rd party websites to fit the advertisement to your interests.
On this website you can check out how unique your browser is and how easy it is to identify and track you.
To make this a bit harder for them and save yourself the trouble of constantly logging in and out I will show how you can create a webapp with an independent profile for your Linux desktop.

It is very easy to create a custom launcher for each webapp and Firefox allows to create multiple profiles since a very long time. So in principle it is very simple and easy!

Let's do a webapp for Facebook! First, create a new Firefox profile, which will be used for the "Facebook-only-Firefox". Therefore, start the Firefox profile manager by typing:

$ firefox -ProfileManager




Now add a new profil 'facebook' and close the manager again. Next, create the launcher by copying the original Firefox launcher to the $HOME directory and rename it:

$ cp /usr/local/share/applications/firefox.desktop ~/.local/share/applications/facebook.desktop

Then we edit the facebook.desktop file and set the launcher name, the icon and the process how the application will be started. I suggest to get a nice icon for your application from the web and save it to ~/.icons/facebook.png. If the folder does not exist yet, create it!

$ vim ~/.local/share/applications/facebook.desktop


[...]
Name=Facebook
Exec=firefox -P facebook -new-instance www.facebook.com
Icon=facebook.png

-P profile-name opens firefox with profile "profile-name"
-new-instance opens Firefox in a new instance, as a separate process
Icon= If the icon is stored under ~/.icons/ there is no need to enter a path!

To immediately see you application in gnome-shell you can press Alt + F2 and type "r" and ENTER. This reloads the gnome-shell. Now you can use Facebook in its own browser, but don't forget to log out in your everyday browser ;)
To hide the tabs and therefore save screen space I recommend the Hide Tab Bar With One Tab addon.

NOTE:
There is one tiny problem you have to consider and which I didn't find a work around yet:
If you start the Facebook webapp and want to open your Standard-Firefox afterwards, it doesn't select the right profile. You could either change the firefox.desktop by copying to it to your $HOME as above and adding the default profile to the Exec line:

$ cp /usr/local/share/applications/firefox.desktop ~/.local/share/applications/firefox.desktop
$ vim ~/.local/share/applications/facebook.desktop


[...]
Exec=firefox -P default -new-instance


or you have to start the default firefox first and then open the webapp. Do you know a solution to this?
Happy socializing 2.0!

UPDATE:
Mozilla develops a webapp framework for their Marketplace that works in a similar fashion like we show here: Separate profile directory, minimal UI, own launcher,... The only difference is that they also create a separate binary and therefore do not have the multi-instance problem. A third-party developer (dietrich ayala) created an extension, "Standalone" which uses this framework to create webapps from any page on the web. Awesome!