The USPTO has moved away from using Tiff images. They are now using PDF files so you should now be able to see the USPTO patent drawings with a pdf viewer plugin such as Adobe Acrobat Reader.
If you are still in need of viewing Tiff images, a free extension "Aspator" by Kenneth Yip was most recently still available that supported Firefox. see http://www.d-publish.com/aspator.php
I briefly used it and can't say much about it.
Prior to that Accel View Tiff was my preferred plug in but the publisher no longer supports it due to the change to PDF documents at the USPTO.