How to disable the marquee tag (text animations) on Mozilla Firefox?

This old help page has a solution that still works as of March 2015:

1. Open Firefox and press ALT to show the top menu, then click on Help → Troubleshooting Information → Open Containing Folder
2. If it doesn't exist yet, create a folder named Chrome
3. If it doesn't exist yet, create a CSS file with the name UserContent.css
4. Copy the following code to UserContent.css and restart Firefox:

/* Stop those <marquee> tags! */
marquee {
   -moz-binding                  : none !important;
   display                       : block;
   height                        : auto !important;
}