Mozilla Firefox problems...?

Mozilla Firefox won't let me copy and paste anything. Every time I try to paste something, a box comes up and says "Copy/Cut/Paste is not available in Mozilla and Firefox. Do you want more information about this issue?" If I click yes, it directs me to a different page. The new page has a headline of "Setting Prefs for the Mozilla Rich Text Editing Demo," and starts off with "To protect users' private information, unprivileged scripts cannot invoke the Cut, Copy, and Paste commands in the Mozilla rich text editor," and then some stuff about my browser settings that I'm still trying to figure out. Does anyone know what is going on?