Checking the Lexmark site, for Firefox it installs the toolbar found here - https://addons.mozilla.org/firefox/addon/lexmark-toolbar/

That toolbar is compatible with Firefox versions up to 3.6, it is not shown as compatible with Firefox 4. You can contact Lexmark to see what their plans are for updating their toolbar.

Try using this extension.
https://addons.mozilla.org/en-US/firefox/addon/print-edit/

It does basically the same thing as that Lexmark toolbar does, as far as allowing the user to edit what is printed - IOW, removing advertisements and other stuff that you don't want on the printed page.