A place to discuss the news and latest developments on the open-source browser Firefox
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.
Sandboxie might help? (For Windows)
Thanks but you should have told me about it earlier
I'm a little confused as to how that would help with privacy/security.
When your browser is open and 'unlocked' a virus could still read the data.
It's the same thing with full disk encryption, if you get a virus on the running system it doesn't matter.
Isn't your computer disk encrypted already?
Otherwise you seem to want jails or sandboxes to protect each app, with access denied by default. That sounds more like Android, or possibly Qubes OS: https://en.m.wikipedia.org/wiki/Qubes_OS
Or flatpak
"full-disk encryption" is the search keyword you're looking for
They refuse to do it because the idea has absolutely no merit to it. If there's a virus on your computer that could steal your data, it can just wait till you unlock that data to steal it. There is zero practical benefit to implementing your suggestion.