Vim filetype plugin for gitrebase

Question

I saw an online snippet for the gitrebase plugin for vim that allows you to easily switch between fixup|squash|pick, etc. for git interactive rebase. The message suggests placing the file in a directory with a name ~/.vim/after/ftpluginand name itgitrebase.vim

I did all this, but the plugin does not load when I execute git rebase -i HEAD~x

What else do I need to do?

The plugin is here if it is useful for someone else: https://bloerg.net/2013/12/04/a-tiny-vim-plugin-for-interactive-git-rebasing.html