Sometimes when I want to watch a video on YouTube while Adblock Plus is enabled it doesn't show the video it's only audio.
Re-Install Windows and Firefox didn't solve the problem.
Screen Record:
https://youtu.be/cE2rk10PgRw
Windows 10 Pro x64 Version 1709 (OS Build 16299.19)
Firefox 56.0.2 (64-bit)
Adblock Plus 2.9.1