On TenFourFox, based on Firefox 45 ESL, the category select is unclickable. I can select a category for the post, but only if I search the category and hit enter.
This isn’t a big deal, and I might be one of 3 people that this is a problem for, but I thought I’d point this out. I don’t know how to show this as when I open grab and go to take a screenshot it deselects the window, and therefore, closes the selection popup.
I don’t have an adblocker installed, nor is the built in one running.