How do I adjust the FONT SIZE on Safari 10?

I can't do anything about fonts (though Kaeve's solution above is incredibly helpful), or poor web page design, but as for auto-playing ads - you might want to check out Adblock Plus.

True, and for many people that will be the solution of choice. For some of us, though, it's a matter of inertia, convenience, and familiarity. Most browsers do basically the same things in basically the same way, so it's not that hard to learn a new one; but Safari has all my bookmarks (many, many bookmarks), knows my browsing history (for better and for worse) and has learned my preferences, so it becomes a question of whether the inconvenience of starting over with a whole new browser outweighs the inconvenience of putting up with Safari 10's foolishness. Chacun à son goût (and I apologize if the non-English characters get mangled in translation).

Much appreciated. Kaeve was actually the first one to post that solution on this thread, and someone (Apple, maybe?) selected that answer as the "Solved" entry. I hope it was Apple - that would mean they actually took a look at this discussion!

My apologies to Harold Holbrook, whose clarification of Kaeve's solution was at least as helpful to a non-techie like me, for being unable to also mark his post as the "Solved" answer; it's clear from the other thread that I'm not the only one who benefitted from a fuller explanation. My apologies also to all the people whose answers I found helpful, because for some reason I have been unable to mark any answers as helpful, either directly on this site or via the e-mail link; not sure why that is (a new Safari bug?), but I guess all I can offer is my verbal appreciation.

JPanimal, AppleMacBrett, and PAWatkins: First of all, I don't know why Apple tells you to simultaneously press the "option", "command", and "+" or "-" keys. As AppleMacBrett observed, pushing down all three keys does nothing, on his MacBook Air or my much older one. The key with the curly four-leaf-clover thing is not the "option" key, but the "command" key; and if you press "command" and "+"/"-" together, it does affect the screen. I don't know whether the keys work differently on a MacBook Pro or an iMac, however.

But [command]+ isn't the ideal solution, at least for me, because it doesn't zoom just the font size. It also affects the size of the whole page, and/or the individual size of various fields, including the boxes which contain the text; on some pages, it alters the fields more than it changes the text size. I may be able to make the text more readable, but on pages where the fields zoom up more than the letters, I end up with lots of wasted space, and boxes that are too large for the text; and if certain fields expand to the point where they are no longer displayed side-by-side, but instead are placed one above the other, I have to keep scrolling up and down to see everything which used to be easily visible on one screen. On other pages, when the text and the whole page get bigger, the page ends up too big for the screen, and I have to keep sliding back and forth to see the whole width. The "Zoom In" command in the Safari View menu seems to work exactly the same way.

The now-deleted "Minimum font size" option, and the equally effective but more inconvenient Terminal command, are the only ways to change the text size without affecting any other features of the page. (Actually, this is only mostly true. There were a few pages where a key button disappeared off-screen when I was using a large font size; the button could only be displayed and used when I made the font size much smaller.)

I have to say, though, that I actually like the fact that the [command]+ function is page-specific. If I use it only for minor adjustments, and use the Terminal command (or Page Zoom) to set the global appearance, then I can tweak individual pages without changing every other page.

Welcome to the Forum! - and I appreciate your taking the time to create an account and offer a solution. I replied to your post and the two which followed, but in case you weren't following the whole discussion, I wanted to give you a heads up; that (much longer) reply should be right above this one.

Hey - how did you manage to create an avatar which isn't one of the limited choices offered by Apple?? Please let me know! My picture (an antique Mac) is not inappropriate, but not terribly personal either.