While slightly off topic, I prefer to use FireFox for almost all browsing, and switch to IE only a site does not seem to "function properly". I mention this as this has limited my use of "Exploder".
Also, setting up a secure connection requires a significant number of software handshakes for key exchanges, etc., which makes SSL somewhat sensitive to network latency. Nice to consider, but this does not address your observation either... Both browsers go through the same pipe. Still, a traceroute to an encrypted and a non-encrypted site may be interesting. I think the first hop might be a big one.
Hmmm, what about caching? If you clear the cache (and cookies) on both browsers, do you get the same performance disparity on a "first" visit to each site? If so, does a "second" visit now work faster on FF? Combined with high latency on your connection, this might explain what you are seeing.
By default, IE7 does not cache encrypted data. If FF does cache by default -- and I don't know if it does -- this could be part of what you are seeing.
Another thought... Are you using any "web accelerator" software? I have seen anecdotal reports this can impact SSL performance.