Example Problem: layout.css.devPixelsPerPx

I somehow had the idea that things in about:config were also configurable via the userChrome.css. Is this true? Is it true, for example, with layout.css.devPixelsPerPx? If so, what is the equivalent CSS selector? Also, will changes to the css file over-rule changes in about:config, or vice versa?

Answer: not much overlap

From It_Was_The_Other_Guy¹, it appears that there is rare overlay between the userChrome.css and the settings in about:config.

No, that’s not true at all.

userChrome.css cannot alter prefs. However, some things that are altered by prefs might also be changeable with CSS. But the pref you mention is not one such thing.

Resources

https://www.reddit.com/r/FirefoxCSS/comments/11xj5w1/aboutconfig_vs_userchromecss/

Footnotes

¹ Reddit https://www.reddit.com/r/FirefoxCSS/comments/11xj5w1/comment/jd3rioz/?utm_source=share&utm_medium=web2x&context=3