I'm using the FastMail web interface more and more recently, but I keep losing the tab I keep it open in.
I found this AppleScript that is supposed to search Safari tabs based on the contents of a URL, but it gave me an error. So I fixed it (and hard-coded "fastmail.com" as the string to search for in the URL). I saved it as a .app file in Script Editor and trigger it with LaunchBar.
Update 1: here's a (low-res) transparent icon pulled from FastMail's website that you can use for the .app created by Script Editor.
Update 2 (January 16, 2015): I've updated the script to fix a few bugs (like the window with the FastMail tab not actually coming to the front), and to automatically open FastMail in a new window if there isn't a current table open.