My time to ask a question! 
I have an animation that uses a few sequences of png files. In one to the sequences, the png files are 475 wide, the Stage is 550. When the playhead reaches this symbol in FF, there is a delay between the off for the first png and on of the second png as well as the off for the second and the on for the third.
Any suggestion on how to correct this? (I had it on the same timeline as the other sequences before and it was not working right so I made it a symbol but it did not make any difference).
The whole animation is also noticeably slower in FF. 