Add / change functionality (ideally improving your friend's work)
Send a pull request to the original author to accept your change
homework
Good & bad extensions:
write 2 ideas for extensions (1-3 sentences each)
One will be a "good idea" - an extension you would like to see available and would like to try out
The
second would be a "bad idea" - as in an extension that would make the
web a worst place and you would rather no one installs or uses (this
could be anything from Facebook Invite All to different flavours of malware)
Start thinking of ideas for what you would want to build