Is there such a thing as a Firefox extension to override a website's preferred fonts, able to be used selectively on individual websites?
(Preferably for Firefox 52 ESR at present, but also for Firefox Quantum in the future)
I know that it is possible to untick "Allow pages to choose their own fonts" in: Preferences » Content » Fonts » Advanced, but this is an all-or-nothing setting, and makes all sites use only your preferred fonts, and so losing much of the design theme of many sites.
Unfortunately, there are some websites which do not design their stylesheets very well to work properly on all platforms, and often, especially when browsing on Linux, the site's "preferred" fonts can be quite inelegant or less readable when you visit that particular website. For such sites (and only for those individual sites, on a site by site basis), it would be useful to be able to override their font preferences to use your own font choice(s) instead.