Mobile browser font sizes
Most mobile browsers (including e.g. Firefox and I think also Safari) "bugger around" with font sizes unless you stick a <meta name="viewport" content="width=device-width, initial-scale=1.0"> tag into the header, because otherwise there's no good way to distinguish between pages that work well with the screen dimensions commonly encountered on a mobile phone, and those that don't.
Pages from the former category can be simply displayed as-is, but for pages from the latter category you can basically choose between
1. Squeezing the page into the narrow width (300 - 400 px) available on a phone in portrait mode (can lead to horrible layout breakage)
2. Rendering the page at a desktop size width (~ 980 px) and then zooming out to make it fit the available screen width (leads to unreadably small font sizes), or
3. As you put it "buggering around with text sizes" as a compromise between the two – it might still occasionally cause some layout breakage, but not as much as 1.) usually does, and in turn font sizes for the main content are usually much more readable than in case 2.)
So in order to reasonably display pages whose layout predates the mobile web, a number of browsers (not just Chrome) choose option 3.), unless a page explicitly declares that "Yes, I work well on narrow screens, too".
Biting the hand that feeds IT
