Have you ever remembered seeing something on Reddit awhile back, but then have a hard time finding it in your browser history or via the Reddit search?
Reddit History is a Firefox and SeaMonkey extension that keeps track of all the submissions you've viewed and lets you filter through them based on sub-reddit and text search (regex). Each reddit user has their own history data.
This add-on is also available as a userscript: http://userscripts.org/scripts/show/63708
No restart required!