Memory increases and Firefox will not close

When using Ubiquity 0.1.8 on Firefox 3.0 and 3.5b4, memory seems to leak and after about 4 hours Firefox is using approximately 600 MB on my system. My Firefox UI will also hang for a second every 10 seconds or so, and when I close Firefox the window will disappear but the process will continue to run in the background until I close it with Task Manager.

My list of installed add-ons:
Remember the Milk for Gmail
Twitterfox
Ubiquity
Weave
Web Developer
Xmarks

I've disabled all but Ubiquity and the problem still happens. I'm unsure what other information I could gather/provide, so let me know if there's anything else that could help to narrow down the issue.