Great, though a bit fiddly to work with: I often use it to manipulate the DOM, so I spend a lot of time switching between writing/testing a bit of code, and inspecting elements with the Dev. Tools window, so the fact that this runs in a little toast and disappears the moment it loses focus is more than a little annoying. I generally end up working in my text editor, and then copy-pasting the changes into the extension when I want to run another test. It would be nice if scripts were managed in their own window, similar to the way Stylus handles working with custom stylesheets (this extension + Stylus = a most dynamic duo).