I'm thinking of creating a Firefox account to use across devices, but I'm not sure how secure it is. It requires my email, and will store my saved passwords and history etc. If possible I'd like to know the technology behind the security so I can see for myself how secure it is.

Also I'm not sure if I need to use Firefox for Android for my phone, or if there is a minimal alternative that won't keep prompting me to choose between Firefox and my preferred browser for things I tap in the phone that resolve to URLs.