"Upgrade your browser" - to what exactly?

[DarrenDev · Accepted solution]

OK, so we can't explain why @GaryF 's browser was reporting an incorrect user-agent, however it was - multiple different browsers, all with really old version numbers. It's now identifying itself correctly, and all is working as it should.

[GaryF]

Note that, as of today, both Chrome and Firefox are now working as expected again, although I've changed nothing whatsoever here, no updates, no software changed, so it's a bit of a mystery as to why it was giving that error message previously.
Note this is nothing to do with the browser user-agent switcher extension I had tried as a work around, as this was only tried on Firefox after the problem appeared.

Thanks for all the replies.