im currently trying to implement a dynamic addon for my firefox addon. I want to add a counter as is used by honey oder AddBlock AddBlock Icon

I cant find any explanation on the MDN developer guidelines on how to achive this though... I know that I can set a new icon using

browser.browserAction.setIcon({path: "/path/to/image"});

but that would require me to create an image for every instance and rescale the image accordingly.