Slither.io Mods for FireFox and related browser (Update 2.1.5)

 

slither.io-mods-firefoxStep 1

Try to install Greasemonkey extensions on Firefox, and Install Tampermonkey on Safari/Chrome
Install Tampermonkey at here.

https://addons.mozilla.org/en-US/firefox/addon/tampermonkey/

Install Greasemonkey or Tampermonkey add-on for Firefox. Download with link below: