Text Rewriter от pelmers

Firefox plugin to rewrite phrases in pages.

Supports any Javascript regular expressions, including backrefs and captures. I just visit the visible text nodes on the page and use nodeValue.replace for each provided pattern. This means if there is an overlapping pair of patterns A -> B and B -> C, then both A and B go to C.

Clicking the icon in the taskbar disables the addon for that domain. For example maybe you went a little overzealous with the substitutions and want to disable it on Slack because of possible... misunderstandings.

Also has an experimental live update feature that will perform replacements on any text that appears even after the page loaded (such as Youtube captions). Enable this from the options page.