lost protocol in url
when working on local sites (ie sites with no domain, like http://myserver/dir1/file.html), FF tends to forget the protocol in the url field (simply omits the "http://"). this is no big deal, unless you click into it and eg. change some filename and send that. then, logically, FF thinks it's a search-string and redirects you to the primary search engine (eg. google) with your local url as the search criteria, which is plain wrong.
Wšykne wótegrona (1)
Try to set browser.urlbar.trimURLs = false on the about:config page.
You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.