I don't agree with this at all. Who said the entire colourblind population knows their browser even has extensions?
If you've got a statistically rare disability, then you acquire whatever basic gear you need to get by in the world. If you're Stephen Hawking, that's a device which translates your eye movements into text. If you're blind, you get a seeing-eye dog, a white cane and a TTD reader/writer. If you're legless, you get a prosthetic limb, crutch and/or wheelchair. And if you're colorblind, you add a simple extension to your browser, or get a volunteer geek to make those 3 or 4 basic clicks for you. If you operate a computer yet don't even know how to do a download, nor install an app or extension, then your issues go beyond that fundamental disability alone, because you just don't know how to use a computer, period.
Up to a certain point some basics are assumed to be a given, and taken for granted: you know how to load your OS. You know how to set up an Internet connection with your ISP. You know how to install an app. And you know how to install a browser extension, esp since it's a basic one-click operation (in FireFox at least).
...which leads to another point: forcing every website within the vast, uncharted and for all practical purposes infinite expanses of CyberSpace to reprogram (sometimes in drastic and aesthetically jarring ways) so as to visually accommodate the unique disability of only a narrow percentage of users is a bass-ackward non-solution. A better way to go is to campaign/ensure that the 3 or 4(?) major browsers out there have preferences settings allowing for color-independent highlighting of hyperlinks. Simple solution, highly effective, and makes sense.