(UPDATED 21 June 2020) I've added a resizer in version 1.2, but unfortunately, Firefox limits this kind of "popup" to 800 pixels wide and 600 pixels tall. The drop-down _should_ automatically uses the full 800x600 if there is enough content and your screen dimensions permit. I've explored using a custom style rule in a userChrome.css file to stretch it further, but no success so far: https://www.reddit.com/r/FirefoxCSS/comments/hbr7xx/any_way_to_enlarge_extension_popup_beyond_800x600/ .