Hello and welcome. :) I'm not sure there is a shorter method than that, unless you stop Firefox from remembering your passwords to begin with:
Choose "tools" menu and click "options".
Select the "privacy" tab on the new window.
Then open "saved passwords" category.
Remove the mark on the check box named "remember passwords".
Click "OK" to continue.
Or, you could use a special software designed to erase your passwords and history for you automatically - there are several of these available on the Web, through a quick search.