I use the USPS web site to print shipping labels, and each time I upgrade to a new version of Firefox or LInux, I always run into the same problem: printing labels doesn’t work. As soon as I click the Pay and Print button, Firefox goes into some kind of infinite loop reading data from the USPS web site, and the PDF file containing the label is never seen.
The fix is to change how PDFs are handled by Firefox so that Adobe Reader is started as a separate process, rather than as an embedded window inside Firefox. Here’s how to do that in version 3.0 of Firefox:
Open Edit / Preferences, then click on the Applications tab. Enter PDF in the search box; a single entry with Content Type of “PDF document” should be displayed. Change the Action to “Use Adobe Reader”; make sure you don’t select “Use Adobe Reader (in Firefox)” accidentally.