Is there any way to run this on mobile Firefox? I've loved this on desktop and installed firefox on my Android tablet but this addon shows as "not available".
I don't think so, I am set up on mobile to use a password safe for account login, then I delete all cookies and state on log out. So when the browser opens, there's usually nothing in it, and then the signing for the site I want to go to is auto filled making login pretty simple, then I quit on close.
Focus is great, but it doesn't handle the use case of having multiple accounts for a site that you don't have to sign in each time to use. Otherwise it's basically a fancy "private browsing" window.
