is an extension for
which lets you run bits of code, known as
"userscripts", on any webpage in order to change the appearance or
behavior of that webpage. Although that may sounds a bit technical it is in
fact a very useful and powerful extension that can be used to resolve
all sorts of problems and annoyances with specific websites or
enhance the usability of websites.
Probably nothing works better at explaining what Greasemonkey can do
than to provide a few examples:
Sometimes URLs are written in plain text (for example on forums),
and you have to copy and paste them into the location bar.
So how about making all URLs on a webpage clickable? No problem, just
The Financial Times requires visitors to log in to read a full article,
but a trivial change to the URL will show you the full article without
requiring you to log in.
Why do this manually everytime, when the
can do this for you automatically?
It may annoy you, as it annoys me, that Youtube videos start to play
automatically, especially if you open several videos in different tabs
at the same time and they all start to play.
Prevent Autoplay script
will solve that problem.
Or maybe you just want to easily download YouTube videos to your own
So add a download link to the page with the
Youtube Downloader script. (details)
If you have a Google AdSense account, it's forbidden to click on your
own ads so wouldn't it be nice to prevent yourself and other
people that use your computer from accidentally clicking on your own ads?
See: AdSense Click Protection
(read the details).
Or... whatever the issue is that you want to resolve:
There is a fair chance somebody else has already written a
userscript to solve your problem, try to search for it on
And finally it's always possible to
write your own
(or ask someone else to write one for you).
It's easy to activate or deactivate Greasemonkey by simply clicking
on the monkey face at the bottom of your browser. However you can also
just activate or deactivate individual userscripts through the menu that
appears when you "left-click" on the monkey face. The menu will show the
userscripts that are active on a particular site (YouTube in this example).
Greasespot - Official Greasemonkey homepage and blog.