Memory & Jank issues (/questions/998289)
I have the same memory issues with firefox as others. It continuously increases its memory usage as long as it is open (as determined by Task Manager) and the only way to fix it is to restart firefox. At over 1GB, firefox becomes very slow to respond. Very, very frustrating.
Try disabling Firebug. Enable it only as you need it and restart Firefox when you're done using it.
The built-in Developer Tools have pretty much eliminated the need for Firebug these days. https://developer.mozilla.org/en-US/docs/Tools