Clicking the Preview button on the Print Edit WE toolbar should display the 'Print' panel with a preview of the printed page and lots of options including an option to set the 'Scale' to a percentage or to fit the page width. You may need to click the 'More Settings' dropdown to see all of the options.

It is possible to revert to the older style 'Print Preview' window by setting the 'print.tab_modal.enabled' preference to 'false' in the 'about:config' advanced preferences page.