I would not have information about non-IE browser preference settings, so the bast I can offer when seeing the following in HijackThis is to mention to you that if you yourself did not set these, then you can fix them with HijackThis (it would restore default settings). I assume you have Netscape also, and although a Mozilla product am not sure how that might interact with FF.
N3 - Netscape 7: user_pref("browser.startup.homepage", "file:///C:/Documents%20and%20Settings/Russ/My%20Documents/Personal/startpage.html"); (C:\Documents and Settings\Russ\Application Data\Mozilla\Profiles\default\wxpl46jr.slt\prefs.js)
N3 - Netscape 7: user_pref("browser.search.defaultengine", "engine://C%3A%5CProgram%20Files%5CNetscape%5Csearchplugins%5CSBWeb_02.src"); (C:\Documents and Settings\Russ\Application Data\Mozilla\Profiles\default\wxpl46jr.slt\prefs.js)