(written by dtolman)
If you already have these installed on your browser, feel free to skip to the next section below.
Firefox: Go to the site https://addons.mozilla.org/en-US/firefox/addon/greasemonkey/
Click on the box +Add to Firefox.
It will download the greasemonkey addon, and popup a box asking you to install. Once the install is done, it may ask you to restart.
Once it is installed you will see a new icon on the top right of the menu bar of your browser. If its greyed out, then its inactive. Click on the icon to activate or deactivate it.
You’re now ready to download a mod and install it!
Chrome: Go to the site https://chrome.google.com/webstore/search/tampermonkey?hl=en
Click on the button next to Tampermonkey called Add to Chrome on the top of the screen.
It will popup a box asking you to add or cancel. Select Add.
Once added you will see the tampermonkey icon appear on the top right of the Chrome browser.
There are two good places to find mods for planets.nu. You can look on the planets.nu site itself under the developer forum: http://planets.nu/talk/channel/developers, and click on individual threads to find mods you may find interesting.
Another way you can find mods is to go to the site that stores almost all mods for planets.nu, http://userscripts.org. On the userscripts site, go to the search box on the right and type in planets.nu and hit search. The planets.nu related mods will appear in the list.
Click on one of the mods that looks interesting, and it will open up the scripts homepage.
Whether you got to the script from the planets.nu forum, or the userscripts.org site, you should eventually end up on a script page. Click on the install button on the top right to install the mod.
On firefox it will popup a box asking to install. Click the install button on the bottom left of the popup. On chrome it will load a new screen, then popup a box with the choices OK and Cancel. Select OK.
It should then install the mod into Tampermonkey (Chrome) or Greasemonkey (Firefox).
Go to the planets.nu site, hit reload (the F5 button on the keyboard in Windows, or the reload icon in your browser bar), and click on the tampermonkey or greasemonkey icon on the top right of your browser.
If the mod is installed successfully and active it will appear in the dropdown list with a checkbox (firefox) or with a green dot next to it (chrome). If it doesn’t have a checkbox/green icon, just click the mod name to activate it, then reload the planets.nu site again to make sure the mod loads.
Firefox with script running