FF is fast on the desktop but still very slow on android. Im not sure what the difference is, but Ive switched to using a chrome fork on android and FFon my desktop and am pretty pleased.
I'd guess he wants to be able to sync bookmarks/passwords/etc across platforms. It's nice being able to find something on my phone and then pull it up later on my desktop using synced bookmarks or Firefox's "send tab to device" functionality.
I will say when I first started using Firefox on mobile it did seem slower, but the ability to use extensions like ublock has always made up for it. I think speed has gotten a bit better lately, but there's still room for improvement there.
The current build of Firefox for Android is being sunsetted soon, last noon security update is going to be in July. The version they are moving to, Firefox fenix is very fast. At the moment I don't think it has sync enabled (so no sign in) but the future looks good there.
Nice maybe Ill go back for Android. I couldnt figure out why it was so slow, its seemed almost like a DNS issue because the first page load, even if it was local, took 10+ seconds. Im a huge FF fan and supporter, I'd like to go back.
Why do you say they work in concert?