I downloaded this new version, compatible with FF57, but the icon that appears in the toolbar is GI-NORMOUS. I loved the old version and suspect I'll love this one. But please fix it, or give me some idea of what I may be doing wrong (if that's the case). (I'm using FF56 with Mac OS 10.11.6.)
I am not sure if I understood the request. All this addon do is, when you click toolbar button this create an overlay on screen and lets you to drag and select and area which gets the size of selected area in pixels.