This isn't actually mine, just something I stumbled on. Before I go and pull this apart to do it myself, does anyone know of an extension that will do this to arbitrary text in Firefox?
I found this because someone was using it as an argument against syntax highlighting for code, but I actually find that it lets me read significantly faster.
You may be interested in BeeLine Reader [1]. It puts a color gradient on alternating lines to text to hopefully let you read faster. I think it works a little bit. When I really want to read an entire article but don't want to invest too much time, especially if it's somewhat fluffy, I'll use Spritzlet set to 700 wpm [2].
Interestingly, when people see BeeLine Reader for the first time, many of them think (incorrectly) that it's a sentence-based algorithm instead of a line-based algorithm. Their belief often persists even after being told (by me, the creator) that it is in fact line-based. We've thought about doing something that's sentence-based, or syntactically or semantically aware, but as others have pointed out those tasks are much more complex.
I found this because someone was using it as an argument against syntax highlighting for code, but I actually find that it lets me read significantly faster.