Tried this on v.88.0.1 and nothing. To eliminate any possibility for interference, I made it the only extension in Private mode and still nothing.

Installed this on the latest version of Firefox (74.0). Set the "change" color to red. It does not change a link color after I visit a web page. ?????

ne fonctionne pas sur firefox 71

Loved it (five stars) until it began crapping out intermittently (3 stars), now it has stopped functioning altogether (1 star).
Firefox 78.1.0esr (64-bit) on a 2017 iMac

No funciona en mi Firefox 56.0.2 64bits

It would be nice for those of us with low vision, if it worked. However it did not work in Firefox 56.0