Bug 4606 is a kind of meta bug for HTML5 performance improvements. However, one thing we could do in near future is to fix this issues:
ie remove the arbitrary waiting times before requesting new updates.
Fixed in revision 27718.
Updated in revision 27816.
A bit tricky to test without a reference point, but I'll assume that the proposed changes have been implemented. One thing I noticed was that moving windows around the desktop is laggy when using a desktop browser, and almost completely unresponsive using iPad.
However, we still have bug #4606 and performance is probably sufficient for now. Closing.