The search function is totally useless.

I am searching for an old post I made on fixing a problem with Firefox overlapping images with tables placed below them. The solution was in the post. But the search function will not find the post.

Instead, it is finding posts that have only one of the keywords I put, instead of requiring that all of the keywords be present.

Agreed.

Here's how I usually find my old posts back:
go to google and type some thing like: site:daniweb.com midimagic firefox overlapping images tables
It's a bit work, but it might help

Yes, the new search function does not work very well. It also finds posts that have been removed.