Used to be favorite, but now... Rated 3 out of 5 stars
Please make this one work in FF 29+ without the need for installing the extra statusbar add-on!
Firesizer used to be my most used add-on: it's very helpful when you change browser window size often to different screen standards. It's also easy to customize.
But I'm consciously limiting the number of installed add-ons, for reasons of browser speed and stability, so really don't need an extra add-on to keep another one working. Also 'keeping alive' the status bar now that it's been structurally abandoned by FF isn't the way to go. So I've stopped using Firesizer for now.
Having a small popup panel (e.g. like Ghostery has), or having the resize options show up in the right click option menu would be great.