Somewhat off-topic, but maybe another editor out there could use this tip.
This bug has plagued me for a very long time now, and so I finally broke down and did a some searching. Through the hwll that is bugzilla I finally found the right bug report: http://bugzilla.mozilla.org/show_bug.cgi?id=252371
And within it was the solution.. using an extension which reverts the find functionality to the older, working, version: http://s93731204.onlinehome.us/firefox/retrofind.html
So if any of you are bothered by not being able to search through your page when you're editing, do check out that extension and visit the bug report to vote on it.
For search and replace functionality, try the search text area bookmarklet: http://wargers.org/home.hccnet.nl/bookmarklets/searchtextarea.htm
This is one of a bunch of things I need to insert into firefox to work around various programmer choices.. but 1.5 is working nicely. I think that this is the last outstanding issue I have with firefox. I'm glad to be able to do regular editing again, without resorting to an external editor just for searching. =p