As i am sure most to all of you is familiar with YouTube, i will be using them as an example for my finding.
I have found that it is not possible to be able to utilize the “Select A Region” tool for the area under the “Save Full Page, Save Visable, My Shots” tiny window at top right (which i will call the ‘screenshot toolbox’ for this example)
As i haven’t done any more research to find possible hotkeys to be able to move this tiny box over when attempting to select a region under it.
I have provided a screenshot of a before/after to give better perspective on what i am explaining.
For Example: I want to take a screenshot of just my personal channel icon, which shows in the top right corner of everyone’s YouTube page if they are signed in. Now with the tiny screenshot toolbox showing over top of the channel icon area in the top right of the page, it is impossible to do so. Being new to it also does not give me option to use keyboard hotkeys to move it nor does it give option to move the screenshot toolbox as i move cursor over it and then click/hold/move.
I believe there should be something added here so that the screenshot toolbox is movable.
I can provide more info or screenshots, details etc if need be!
Hope this helps and thanks for giving me the privilege to help with the Firefox Screenshots Beta. 