The weirdness between VS dev server and IIS
Every once in awhile I find some strange differences between IIS and the ASP.NET dev server that comes in Visual Studio. The previous item was that IIS seems to have at least two instance of HttpModules, while the dev server only has one.
The new one I noticed tonight I think has something to do with page caching, or at least how Firefox responds to the two servers differently. I have a link button in my forum app that marks a forum as "read," which does the data piece, then does a hard redirect back to the page. (I realize this probably isn't necessary, but I'll revisit that at some other point.) Firefox, however, has the version of the page with the "new posts" indicators still sitting there. If you refresh the page, you're golden.
It doesn't even happen consistently though, which is annoying, and it doesn't happen at all in the VS dev server. Little things like that make it a little harder to really be sure that what you're doing is what you'll get in production. It's rare, but the idea sits there and torments me. :)