Text Rewriter
Rewrite customizable patterns in a page. Created mostly for personal amusement, inspired by XKCD #1288 and "cloud to butt." By default provides a sensible "mispell" -> "misspell" replacement. Also in Chrome: https://goo.gl/r1FXGf
What is Text Rewriter?
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Summary
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.
User reviews
Safety
Risk impact
Text Rewriter is risky to use as it requires a number of sensitive permissions that can potentially harm your browser and steal your data. Exercise caution when installing this add-on. Review carefully before installing. We recommend that you only install Text Rewriter if you trust the publisher.
Risk likelihood
Text Rewriter has earned a fairly good reputation and likely can be trusted.