I made my computer top of the line... in October 2002. It still works fine for web surfing and eMail so I haven't felt the need to make a new one until it actually explodes (although the AGP-4x GeForce 4 Ti-4600 exploded after 8 years and was replaced with a Geforce Fx 5200). Also the PS/2 keyboard port blew out, and Windows XP will be abandoned in April so I guess I'll have to make another one soon. :'(
The biggest problem with this game is that it SUCKS ALL YOUR RAM. It fails to release unused ram in a timely manner. Any competent programer would call that a MEMORY LEAK. This might be a problem with Flash itself, but it might also be a problem with the game code not FORCING Flash to search for and release unused memory.
In Firefox, after about 5 manual missions, it uses your WHOLE Gig of ram and stops DEAD for at least 2 to 5 minutes while the page file accesses. When IE uses your WHOLE Gig of ram it gradually gets slower and slower in a much more elegant way and gives you time to finish the mission and then reload the game. This is probably the only time in history where IE is superior to Firefox.
So it's IE (for this game only and nothing else).
It might also help you to turn off all the visual effects and stereo sound as well.