The "transferring data from ..." box does not go away while viewing videos in full-screen. How do I turn this off entirely?

Please consider turning send info to Mozilla from with in Firefox before posting. Being able to check your Video Card Drivers for errors helps. But no info so guessing. Update Video Card Drivers. Please be aware that Win 10 can and will change your Hardware Drivers to Microsoft's. Check Device Manager to make sure. https://www.howtogeek.com/302595/how-to-stop-windows-10-from-automatically-updating-hardware-drivers/ Update Sound Drivers that came with PC 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 you should make a back up before you do : https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles Reinstall with Current Release Firefox 57.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/ Please let us know if this solved your issue or if need further assistance.