Meta No User-Scalable Autor: Piggy Gaming

adds the <meta name="viewport"> with values width=device-width, <initial-scale=1.0>, and no-user-scalable=0 to prevent Firefox's mobile double-tap to zoom feature.

Source Code

All credit goes to "imheinrichlunge" for the original extension. I have modified it to remove the double tap functionality too, as well as adding the meta viewport tag. See the original extension here<a