Q: How do I adjust the FONT SIZE on Safari 10?

Safari 9 allowed me to increase the font size independently of page zoom, but Safari 10 removed that necessary function. My impression, not being particularly tech-oriented, is that different web pages use different display systems to set the relative proportions of text size, image size, and field size (e.g. a box in which certain text is displayed); and some of these systems interact in odd ways with different browsers. I'm not familiar with Firefox or Chrome, but you might check to see if there is a "font size" control hidden somewhere in those browsers; if there is, you should be able to increase the text (on most screens) to something more legible. The trade-off is that the text may end up too big for a particular field, in which case it will be truncated, or will wrap around, and may crowd out other text; but that's a choice which should be left to the user, rather than having the developers decide what's best for everyone else.

Apple's System fonts have always been teeny, and I've learned to live with them; I don't think they shrunk appreciably with Safari 10. Safari 9, however, at least allowed users to adjust most other fonts, so web pages were easier to read.

A shame they didn't bother to check out this thread - we've already tried and discarded their "fixes", and explained why their suggestions don't work. As you say - no help. (And I'm always apprehensive when Apple's own people say "I've been told", as if they are as clueless as we are!)

"We can do a SMC and a Nvram reset. Both require a restart so we will have to end the chat."

Translation: "Well, gotta run, bye!"

Appreciate it. Let us know if you find anything useful - especially something which can be easily implemented by non-techies like me.