Does anybody know if there is some way to run a piece of Javascript code for each page that loads in a browser? Sort of like inserting <script> first thing inside the head tag. I am most interested in a solution for Chrome. Maybe that is a job for a Chrome extension?
Check out Tampermonkey, it's a Chrome extension for running user scripts (equivalent to GreaseMonkey for FF). To run a script on every page, you'd have a line like this near the beginning of your script:
// @include *
Here's a tutorial on writing user scripts.