evaltool by memdmp

FOR DEVELOPERS ONLY!! IF YOU'VE BEEN TOLD TO INSTALL THIS, SOMEONE'S TRYING TO PHISH YOU! See https://en.wikipedia.org/wiki/Self-XSS

This addon lets you test small snippets of background.js extension code in a persistent environment, allowing you to do things like open specific websites in pop-ups instead of as tabs (https://git.estrogen.zone/evaltool.git/tree/examples/open-loopback-as-new-window.ts).
For just modifying your browser's HTTP requests and responses, you may want to see https://addons.mozilla.org/en-US/firefox/addon/httptool/.
Source code is at https://git.estrogen.zone/evaltool.git
Note: Most permissions are marked as optional. If something doesn't work, it's more than likely that you need to enable a permission.