I have upgraded to Firefox 3.5 and the following is the code that seems to work pretty consistent for me:
<DELAY Flags="\x02" Time="500"/>
<GET PIXEL COLOR Option="\x01" Rel_To_Screen="FALSE" X="139" Y="70" Destination="%StopColor%"/>
<REPEAT UNTIL Variable="%StopColor%" Condition="\x01" Value="197042"/>
<GET PIXEL COLOR Option="\x01" Rel_To_Screen="FALSE" X="139" Y="70" Destination="%StopColor%"/>
<END REPEAT/>
<MACRO RETURN/>
I'm basing the code off an assumption that the X is either going to be red (197042) or gray. As long as it is red, I'll wait.
I haven't had any hangups in the three days that I have been using now.