Perhaps it's downloading updates, as of it's beta?

I would think it is a bug. You could report it : https://bugzilla.mozilla.org/ Please uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But am not trusting so please : https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles It may detect your profile and only offer a Refresh. Installer is also a updater. Reinstall with Current Release Firefox 57.0 with a Full Version Installer https://www.mozilla.org/firefox/all/