is a Mozilla Firefox extension that allows users to install scripts that make on-the-fly changes to HTML web page content on the DOMContentLoaded event, which happens immediately after it is loaded in the browser (also known as augmented browsing).
scripts are persistent, the changes made to the web pages are executed every time the page is opened, making them effectively permanent for the user running the script. Greasemonkey
can be used for adding new functions to web pages (for example, embedding price comparisons within shopping sites), fixing rendering bugs, combining data from multiple webpages, and numerous other purposes.
Greasemonkey 1.12 Website - Greasemonkey 1.12