I've always wanted to have line numbers prefixed in code blocks on questions / answers.
This userscript takes the code-blocks on the page, and inserts line numbers.
It will look at the length of the code block to determine the required additional padding, so a short code-block wouldn't have too much whitespace to allow for 3-digit line numbers.
The best way is to leave a Github Issue for feature reqs, issues, and anything related to the userscript.
The code is on Github