JavaScript is enabled in Firefox's built-in PDF viewer by default, but it doesn't have the sophistication of a full stand-alone PDF reader. If the script doesn't run correctly in Firefox's viewer, you might need to download the file and open it in Preview or Acrobat. ''To check on the setting:'' (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button accepting the risk. ''More info on about:config:'' [[Configuration Editor for Firefox]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''pdfjs.enableScripting''' and pause while the list is filtered (3) If the preference is bolded and has a value of false, double-click it (or click the Toggle button or Reset button at the right end of the row) to restore the default value of true