Yep, I didn't have to do much other then doing if(chrome.contextMenus){...} to make this extension run on Firefox and Firefox Android. But I intentionally chose

Yep, I didn't have to do much other then doing if(chrome.contextMenus){...} to make this extension run on Firefox and Firefox Android. But I intentionally chose the <iframe> approach to minimise the browser-dependent surface, so the <iframe> draws the UI and the extension only makes a few basic things like updating the icon color.