I also endured the 'Sluggish Firefox' period not too long ago.
Something happened with the latest release. It's back to reasonably 'frisky' for me.
I am also using version is 3.6.13 if that helps at all.
And you are right, Chrome *rocks*, but I am so used to Firefox now
Try uninstalling FireFox, restart the system, and re-install. This has worked for me on occasion.
I find it odd that with the same version you are sluggish, and my performance has improved.