StockTwits, a startup that aggregates stock-related “tweets” on micro-messaging service Twitter, has released a Firefox extension that links stock tickers to the StockTwits site. Fred Wilson of Union Square Ventures (a Twitter investor) says he’s impressed by the extension, also argues that it provides a model to make Twitter smarter.

The idea behind the extension is pretty simple — once you install it, all tweets in the ticker format ($GOOG, $APPL, etc.) become links to the relevant listing on StockTwits. (Weirdly, the links only show up in a list of multiple tweets and disappear when you click on a specific message. I assume that will be fixed soon.) [Update: Looks like it’s fixed.] That’s an obvious plus for the startup, since it pulls users back to its site. Wilson says other Union Square portfolio companies — such as Zemanta, which recommends relevant content for blog posts, and Adaptive Blue, whose products include Glue, a Firefox extension that lets you see what your friends thought about things you find online — could follow suit. They would use their semantic technology to create other relevant links within your tweets.

I really like this idea; the StockTwits extension underlines the opportunity that Twitter provides for these kinds of companies. That opportunity isn’t limited to Union Square’s portfolio, either — for example, it would also be a great fit for MashLogic, another browser extension that inserts links based on your interests. With its 140-character limit, Twitter is an environment where the usefulness of any service that helps you squeeze more information into a small space (such as TinyURL) increases exponentially. Within Twitter’s constraints, the usefulness of something like MashLogic becomes much clearer. I’d also guess that both Twitter and these browser plugins need to target a similar early-adopter audience.

Yesterday, VentureBeat’s Eric Eldon outlined how Twitter’s potential is tied to its ability to connect to other web sites. It’s time for Adaptive Blue, Zemanta, MashLogic and others to start exploiting that potential.