For anyone on Firefox getting the "Firefox freezes up while loading the archive" thing, it's because of the way the log is currently handled. What it does is have a script set to continually load up the archive until it's fully loaded. However, while it's working, this script doesn't talk to the web browser at all. Firefox detects this as an unresponsive script, and either asks you if you want to continue it, or, if you mark the check box to tell it not to ask again, it will just let it run until it's done, but it will be occupied keeping track of the script, as well, so it can't do anything more. If you have a particularly large archive (like the campaign I'm in does) it can take 5 or 10 minutes to load it. Just wait it out, and it'll load up eventually.
To the devs: This could probably mostly fixed by either having the archive load in single "pages" at a time (instead of the whole thing at once) that need to be "turned", by having the script talk to the web browser with a progress update every now and again, or by having the option to load the chat archive from the end, instead (because how often are you going to need stuff from the beginning of the campaign?).
Another option would be the ability to clear the chat archive every so often. Perhaps a GM-only thing where they can step over and just empty it out so that anything new doesn't take a long time to load up.
EDIT for clarification: When I say "page" I mean, basically, it would load up to a certain number of messages at a time, then stop until you change the page. Then it would load the messages from that page, then stop when they're loaded. And so on. Basically like a forum thread.