Recently (most likely coinciding with the 50.0 update), Firefox abruptly stopped loading any tabs. All pages get stuck on "Connecting..." including system tabs such as about:support and about:config. Google.com and other Internet sites as well as internal intranet locations do not load. The first tab that opens when Firefox is started will sit at a blank page indefinitely, failing to load the shortcut "speed dial" page. Not even system tabs such as about:support will load. If a second tab is opened and the first tab is closed, then system tabs become accessible, but Internet locations will still become stuck at "Connecting..." This troubling behavior started popping up across dozens of workstations in our organization. On all of them but one (so far), we were able to resolve by getting about:support to load using the method outlined above and refreshing Firefox, which leads me to believe there's some kind of issue with the profile. On one workstation, Firefox appears to work after a refresh, but after that instance of Firefox is closed and a new one opened, the issue re-asserts itself. Upon opening Firefox under a new user profile, it works once before breaking. On this particular station, I have attempted uninstalling Firefox and reinstalling it multiple times to no avail, as well as installing Nightly, which exhibits the exact same issues as the regular build. I'm stumped on how to resolve this issue for the end user. I've even tried running CCleaner. Any ideas?