When using Quicktime viewer in Firefox the control bar at the bottom of the console is usually blacked out and the controls are invisible. Curiously they do show very occasionally. Anyway here is a fix.
1. Right click on the browser icon the main icon on your Desktop of in tool bar not the one at the top left of the browser window.
2. Select properties
3. Go to the compatibility tab
4. Check the box for "Run this program in compatibility mode for:"
5. Make sure it says " (Service Pack 2)" in the drop down list.
6. Press "OK" at the bottom
7. Reload Firefox
This solution will allow you to see the normal Quicktime timeline and volume options, etc. when watching a Quicktime video.