This is the case now: browsers are scriptable and every major browser has the ability to install extensions to adjust nearly every single feature of a page's text rendering with just a few clicks.
Turns out most people just don't care about typography.
"to install extensions". This is satire, right?
There are just two little config changes that obviously no-one would ever care about that make a lot of newer websites unusable: Setting a minimum font size and/or forcing your own default can cause text to pile up, grow to insane sizes, screw up column width that content becomes a tiny ribbon, or cause text to render entirely offscreen. One of the main causes is the same kind of control freak design that insists on low-contrast text - designers who want some kind of pixel-perfect "responsive Photoshop" that ensures no user anywhere can deviate from their choses appearance. The other is forced fonts including icon fonts - designers are not better at figuring out what fonts a user finds most readable (especially those with poor vision) and icon fonts require turning off the users fonts and often enabling javascript.
The new reader modes that browsers are adding let you kinda do this.
Hah, good one. This is the Internet we deserve, not the one we need.