I was up late one night, and my brain was in one of those modes where I needed a new, really quick project to distract myself from what I was currently working on. Sometimes that kind of thing helps the brain to get to a better solution.
I noticed someone on Reddit by the name of hokku was looking for an extension to randomly choose a bookmark and load it on new tab/window instances. I took 20 minutes and knocked this together. It's open source, as I have zero interest in maintaining it; feel free to learn from it to build your own, or fork it and run with it as you see fit. MIT licensed.
Download it, unzip it somewhere, load it up in your extensions tab by loading an "unpacked" extension.
Email: ryan [at] venodesigns dot net
Twitter: @ryanmcgrath
Web: Veno Designs - Personal Site