We've featured quite a few clipboard managers here at Lifehacker, but reader Java-Princess shows us that you already have one built in to your browser: the Firefox search box.
If you select and copy a chunk of text and paste it into the Firefox search box, Firefox will remember this till you clear your search history. You can recall this text at any time by typing a word, or part of a word from the text into the search box. It doesn't even have to be the first word. Then just copy the contents and you have your original block of text.
This in effect mimics the clipboard with multiple items found in MS Office and other programs. It's nothing new, just a new use for a feature.
Sadly, this doesn't work in Chrome as it gets turned into a Google search with %20s and such, nor does it work in IE9 - which gives a 'helpful' message that it can't find the search item.
Still a pretty neat feature for Firefox users, especially since you can already use the address bar to do Google searches. You can use the little search box exclusively as a clipboard and not have it intermingle with your actual search history.