Hi, everyone!
You probably heard of Dogeforces extension for chrome, but there is no one for firefox. So, I decided to make a tutorial.
1.First, you need to install greasemonkey add from https://addons.mozilla.org/en-US/firefox/
2.Now ,you should have a monkey in right-up corner of firefox. Click to expand and click new user script. Fill name tab dogeforces and namespace with http://codeforces.com. Leave blank the rest and press ok.
3.Now, you should have a text editor opened by greasemonkey. Copy and paste there the dogeforces script (dont delete the comment!!)(taken from github) : https://raw.githubusercontent.com/ngthanhtrung23/DogeForces/master/doge.js . Now save and close the editor.
4.Now refresh codeforces and enjoy!