Cannot scroll in Firefox DevTools' Style Editor using scrollbar thumb

I have just started using the Firefox Developer Tools. When I am in the Style Editor, I can't seem to grab the scrollbar thumb to scroll through my style sheets. I assume I'm missing something but can't find what. I have restarted the developer tools, and restarted Firefox, but that didn't help.

My cursor stays as if it is selecting text, even when I hover over the tiny scrollbar thumb, thus it doesn't let me grab the it. Obviously this is important as style sheets can have many lines!

I am using Firefox 50.1.0 currently.

Solution

This is a known bug filed as bug 1265807 .

A workaround for this is to switch to the Firebug theme, which uses the OS default scrollbars: