Well there already is a addon that does this called AddOmmmm.
Link: https://addons.mozilla.org/en-us/firefox/addon/addommmm/

It's making fun of the European Horse meat scandal. It turns the pages upside down, makes horse noises, shows a picture of lasagna and plays meditation music randomly. :D

Check it out! I think you will like it.

If you want to create your own addon and you don't already know how to make one, you won't be able to make one in time for April Fool's Day. It takes time to learn how to make a working addon.

Hey,

if you indeed use my add-on, please hide the toolbar button so there'd be no way of turning it off:

1. Right-click next to the Navigation toolbar, select Customize.
2. Now, move the toolbar button from the Navigation toolbar back to the Customize Toolbar dialog.

And, as always, I'd appreciate a small donation if you found my add-on useful. Since it hasn't gotten full review, you can choose to send in a donation for some other add-ons of mine, instead: https://addons.mozilla.org/en-US/firefox/addon/centersvg/?src=userprofile ;)

Cheers!

--Tobbi (the guy who came up with the totally senseless idea of this add-on).