When abroad, I've programmed myself not even to bother going to google.com any more; I go directly to google.com/ncr (
No
Country
Redirect ) which bypasses the locale detection and loads the US, American English edition.
My Google Toolbar is in the far right of Firefox, to the right of where you enter a web address.
Ah, then you don't have the Google Toolbar, which is bit of software that is installed separately with buttons for various Google-affiliated widgets (GAdgets?). You have Firefox's search box, which is a completely different beast.
The search settings are stored in the "searchplugins" folder in your Firefox installation folder (e.g. \Program Files\Mozilla Firefox\searchplugins). This is a hypothesis, as I have no way to test it here, but you could try editing google.xml (called google.src in FF1). The line that specifies the search URL is <SearchForm>http://www.google.com/firefox</SearchForm>; try changing it to <SearchForm>http://www.google.com/ncr</SearchForm>, saving, and quitting and restarting Firefox and see if that forces the issue.