I've used Gmail on 4+ machines in a variety of browsers and have never ever seen that. You must be in the darkest A/B test timeline.
Edit: Got confused. It's Chrome no longer having updates because of Vista on an old laptop.
I also tested with Firefox, but it seems they stopped pestering us FF-users now. For a long time though every single page owned by Google on the entire internets told Firefox users to "Upgrade your browser" (and yes, those words).
Guess once if by "upgrade" they meant to a new version of Firefox.
And then guess which browser my non-technical parents are using now, after I instructed them specifically to use Firefox to avoid problems?
Can you guess which company is now harvesting all their browsing data?
Do no evil indeed.