Could you try this out and let me know if it works...
Mac FF has a problem / difficulty with fixed positioning. Changing this to absolute might solve the problem.
your current code:
Code:
um.orientation = [
"vertical", // alignment ["vertical"|"horizontal"|"popup"|"expanding"]
"left", // h align ["left"|"right"]
"top", // v align ["top"|"bottom"]
"fixed", // positioning ["relative"|"absolute"|"fixed"|"allfixed"]
"3em", // x position ["em"|"ex"|"px"|"0"]
"220px", // y position ["em"|"ex"|"px"|"0"]
"1000", // z order ["0" to "10000"] (menu takes 20000 headroom)
];
change the "fixed" to "absolute"
Code:
um.orientation = [
"vertical", // alignment ["vertical"|"horizontal"|"popup"|"expanding"]
"left", // h align ["left"|"right"]
"top", // v align ["top"|"bottom"]
"absolute", // positioning ["relative"|"absolute"|"fixed"|"allfixed"]
"3em", // x position ["em"|"ex"|"px"|"0"]
"220px", // y position ["em"|"ex"|"px"|"0"]
"1000", // z order ["0" to "10000"] (menu takes 20000 headroom)
];