FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files. Now you can easily synchronize your office and home browsers.
Not perfect, but the best multiple-session-in-one-browser solution I know of: "CookieSwap is a Firefox/Mozilla extension that enables you to maintain numerous sets or "profiles" of cookies that you can quickly swap between while browsing."