This is from a slashdot article on Greasemonkey, the Firefox plugin that lets users tweak sites they visit (and which actually bears a resemblance, I think, to something I proposed 4 or 5 years ago when I was more involved with Mozilla) with scripts. Someone comments, well, see here:

Google has tried something similar before with their toolbar and ISBNs.

That said, I am going to use this guide to disable Greasemonkey 1.
I write websites so I can present ideas to people. I don't want them to see my
site the way they want to see it. I want them to see it the way it was meant
to be seen. That way I can provide content based on expectations of standards
compliance.

If you want to display my content with your own formatting, use
my RSS feed 2.

The first reply is very amusing.

 Achtung! You vill sit in ze CHAIR ven you read my book, NOT ON ZE COUCH!!!