[aasasd]

The Stylus addon is a more generic solution, it works on phones: https://addons.mozilla.org/en-US/firefox/addon/styl-us/

As a bonus, you can fix the ‘[-]’ comment collapse link by making it five times wider. And crank up the font size.

The primary annoyance with this approach is that you can't look up the tag hierarchy and classes on a phone, at least I haven't found an extension that would let me do it even on the desktop (even though I think I've seen some, years ago).

[anderskaseorg]

An even larger hammer you can use is injecting arbitrary JS using Violentmonkey; that lets you do pretty much anything. It also works on phones.

https://addons.mozilla.org/en-US/firefox/addon/violentmonkey...

[aasasd]

I'm using the classic GreaseMonkey, but I find that my attempts don't match Stylus: the styles get applied after the page is already loaded, so everything is reformatted and jumps away from my view (in cases of heavier formatting, e.g. changing fonts). So basically, Stylus encapsulates accumulated knowledge of properly applying styles in an extension. Plus, it can change them without reloading the page.