I just discovered an addon for IE I didn’t know about, Find As You Type. Even better, Sven Groot, the developer has some technical notes up on the under-documented issues he ran into while developing it, the solutions he found, and the source code to the add-on.
The add-on itself looks like it brings a lot of the useful Firefox functionality I love for in-page searching to IE, including highlighting all terms, and searching as soon as you start typing.
In a nice twist, I actually discovered this using the me.dium Firefox extension. It’s been a fun social tool, but in this case it figured out that the site was related to the MSDN extensions forum I was browsing, and showed it on the radar. Very, very useful, great job by the guys who wrote that algorithm!