Greasemonkey is a Firefox extension that allows you to customize the way webpages look and function. Hundreds of scripts are already available for free. And if you're the tinkerer sort, you can also write your own.
Greasemonkey can be downloaded from Greasespot.
GM4IE is a Greasemonkey implementation for Internet Explorer, but it is not fully compatible with native Greasemonkey scripts. IE7Pro is another Greasemonkey port for Internet Explorer.
Please note, that the devs don't support scripts. If you encounter bugs while running a script, turn off the script and look if the bug still occurs, before reporting the bug. Don't waste the Devs' time!
Don't use scripts that give you access to pages, that you can't enter normally (and no, that doesn't include link manipulation, which is always bad)!
Don't use scripts, that have to gather data from the site instead from the cache, this puts a strain on the server and are very much frowned upon!
Also read following community news on this issue:
Developer News 2008-01-15 Bad Scripts & Banana Peels All players who use bad scripts which constantly trigger pages they shouldn't will see their characters slip on banana peels and hurt themselves. They will continue to fall on banana peels with regular intervals untill the bad scripts are deactivated. Read More» We're not out to get anyone and there's no ill will behind our actions here. We simply want to spare our heavily burdened servers from having to deal with these pointless page views. So if you all of a sudden fall on a banana peel please deactivate the scripts you're using. It's doing stuff it shouldn't without you knowing about it!
Developer News 2007-08-27 Play it safe. Don't use scripts! If you're using any kind of script to “enhance” your player experience you might want to read the rest of this text. Read More» Browser scripts, like greasemonkey tools etc, are frequently developed by cheaters to do things in the game which aren't meant to be done. Most of you have no idea what the scripts you're using actually do “behind the scenes”. You could be trying to cheat, or aid cheaters, without knowing it. Since it's impossible for us to determine if someone is using nasty scripts on purpose or not we have no choice but to treat all players who use these nasty scripts as cheaters. So consider this a fair warning: we will start cancelling player accounts trying to trick the system in any way by using these scripts. Popomundo was made to be played without external scripts of any kind. There aren't any official scripts around and we've never recommended the use of such things.
Developer News 2007-03-29 Player Created Scripts in Popomundo If you're using and/or coding scripts not supported by the creators of Popomundo please read the following. Read More» Generally we're against these scripts. However we realise a lot of you enjoy these scripts/functions which we haven't had the time to create ourselves or decided not support for one reason or another. We don't want to be jerks about stuff like this but the bottom line is this: If these scripts start to burden our servers, interfere with our business model, cheat, or alter the overall gameplay we will be upset and ultimately forced to take action. If you're going to create a script which you suspect us devs might have a problem with please get in touch with us and we'll offer you our thoughts on the matter. Please respect these wishes on our part and don't slow down the development of the game even more by forcing us to counter your work. INSIDE SCOOP: If any scripts look up more than one page at a time to scan the site for information or update more than one thing at a time. Chances are we won't like it. These things usually strain our servers in ways we don't like.
Developer News 2006-12-31 Using plugins and scripts We've had a quite large amount of “bug reports” from people using home made browser plugins recently. This steals time from the dev team and consequently from our users as well, since we spend time investigating “bugs” instead of developing new features. Once again we'd like to remind you that we don't support the use of such scripts and will not spend time on rewriting the code of our webpages for that matter.