Webpage opened on one sceen not displayed properly when moved to the other screen

Setup: imac 5K Retina with a secondary LCD screen attached via thunderbolt-HDMI interface Two problems were noted after Firefox updated version 38.0.5: 1. Problem #1: When I open webpage on imac (primary screen), it opens OK, then if I move it to the secondary screen it does not display properly. Looks like a second copy of the same page 1/4 size of the original is superimposed on the upper left corner. See Attached screen shot #1 2. Problem #2: When I Open a webpage on the secondary screen, it opens ok (see #2 sceen shot) , then if I move it to the primary screen (imac), it is not displayed properly. Looks like the page is displayed on the primary zoomed in. See attached screen shot #2 (on secondary screen) and #3 after being moved to the primary screen (imac)