In the question https://stackoverflow.com/questions/33907611/controlling-line-spacing-with-br-firefox-rendering-differences-with-html4-doc, I wanted to show the boxes of HTML elements, as that would have clarified the problem best. Unfortunately, I couldn't find a way to select multiple elements when using the Firefox inspector, so I had to select each element individually, take a screenshot, and then combine the screenshots into an animated gif like this:

... which is a rather tedious and time-consuming job.

Is there a way to do a multiple selection - either from the main browser window, or from the HTML tree in the inspector in the bottom - such that the element boxes of the selected elements are all indicated/shown simultaneously? I tried Ctrl+click-ing, that doesn't work...

Alternatively, is there another addon/browser/tool that can do this (maybe Chrome?)