I think i need to make myself a little clearer! There are no massive rendering issue.
The primary issue with EE control panel on new Firefox is when using the menu and their drop downs. Click “content” and try and run the mouse from there into the dropdown menu, it disappears.
Having seen this a million times before (when building dropdowns) it is as though the drop down box is positioned a few pixels below the actual button, and so you are no longer on the active button for a tiny area, hence the menu does not think it is active and hides the drop down.
This sounds minor, especially as it is very much hit and miss. But when using the control panel this drives you nuts often having to take 3 to 4 attempts to get to the submenu item you wanted.
The other comment about the Nav-EE menu items - is just a bad case of how it interprets background shadow, and this is not EE that has the problem, just the nav-ee style. But that is for nav-ee to sort… see screen grab attached.
but it is the dropdown menu that i hope they will look into…