The program is not totally portable, it can't run multiple instances of Firefox out of the box.

The web cache and browser history were previously disabled under the release of 2.0.

Firefox Portable's ability to delete cookies and the download history on exit is not enabled by default, as per a licensing agreement with Mozilla.

Personal settings, bookmarks, and any installed extensions and themes are stored on the flash drive along with Firefox Portable.

Plugins such as Flash Player and Shockwave Player cannot be installed to Portable Firefox in the usual sense, but the plug in files can be copied from a local installation to the appropriate portable folder.