Text "gamma" too weak in <=10.9 making text on some sites barely readable

[RJVB]

I've mentioned this before; Apple made a change to the default font/text rendering "gamma" after 10.9, ideally requiring a compensation in 10.9 and earlier to keep the text readable (and rendered as intended by the site).

Consider these screenshots of https://www.atelier-lumieres.com/fr/douanier-rousseau :

In Firefox Dynasty 135.0.1 on 10.9 :

In FF Dev. Edition 135.0.b9 on Linux :

In FF ESR 78 on OS X 10.9 :

And text with colour #212529 in TextEdit: