Chrome does not do it either but are we supposed to be the ones that start a new trend or the ones that follow the trend?
I made a post into their feature request section about how important it is for privacy and security. It is perfectly possible to do but they are not interested in doing.
What I asked was that they provide a feature that allows users to opt in to encrypt all browsing data including history, passwords, cookies, etc. With this feature I can only access my browser information after I open up Firefox and provide my encryption password.
How would this help? Well, there could be viruses that can read Firefox browsing history and cookies and send that to the server. With this feature enabled, one can be even more safer.
There is an option to encrypt Passwords. Thats not enough, every other piece of browsing data should also be encrypted.
To protect it from ... what attack are you stopping here? If you don't know, and it sounds like you don't know, then forget it.
If someone roots your device, you still lose. If someone takes your device while you're browsing, you still lose. If your hard drive is unencrypted, you still lose.