With fingerprinting it's not impossible. Quoting a recent Webkit thread[1] in which Google blocked all sign in from non-Safari WebKit browsers:
> But if Google does this properly and uses more sophisticated browser
fingerprinting techniques, Epiphany is done for. This could be an
existential threat for non-Safari WebKit browsers. Nobody is going to
be interested in using a browser that doesn't support Google websites.
Google's expressly-stated goal is to block embedded browser frameworks
and non-supported browsers from signing into Google accounts. The blog
post says: "This block affects CEF-based apps and other non-supported
browsers." It says: "We do not allow sign-in from browsers based on
frameworks like CEF or Embedded Internet Explorer."
Even if technically impossible, by simply not supporting it - which is already happening - FF will just lose additional market share. I'm at a point where I keep an additional Chromium installed along with my nicely configured FF, because of how many sites doesn't work.
