Me-like-words is a firefox extension that replaces words.
To words.csv, add the word to replace and the word replacing it.
from,to
replaceme,imreplaced
ex1,ex2
I,me
After changing the words.csv file, open Firefox and load the about:debugging#/runtime/this-firefox page. Click Load Temporary Add-on and select the manifest.json file within the Me-like-words folder.