Just switch extensions.pocket.enabled to false in about:config Whole thing gone. It's like an internal addon an that switch disables it.

So what does the braille in the source code comment mean?

Install Stylus https://github.com/openstyles/stylus/ (and fall in love with it), then install a style (e.g. https://userstyles.org/styles/97106/ ) or write your own.

Freestyler might work. https://github.com/openstyles/stylus/wiki/Stylish-Alternativ... Don't know if it's maintained and can be trusted.

Not really. Though, https://openusercss.org/ is in development right now. freestyler.ws is an unmaintained copy of userstyles.org

You must have done something wrong, of course the applied domains are also transferred. Maybe you didn't use the export function but just copied the source?