Most likely that the profile databases were in need of an optimization. Creating a new profile is one way of doing it, since databases are re-created. Additionally, old profiles might have less than optimal prefs settings. Some time ago I used an extension to delete old Preferences, left behind by uninstalled add-ons. It improved page loading considerably. So, creating a new profile would also help.
If you want to try, you can create a new profile, without deleting the current one. To do that, start Firefox with:
That will launch the profile manager.Code:firefox -P
Keep in mind there are other ways of optimizing Firefox, without creating new profiles. Check my optimization tutorials at http://www.webgapps.org/tutorials/firefox