Just delete the folder as it is not really installed. Note that your Profile settings is there also.

Are you deleting Firefox portable for a specific reason (like to troubleshoot it). If you'd like, using regular Firefox is often more reliable, you can download and install it from www.getfirefox.com (you need to update anyway)

SOLVED and TY

FYI, portable applications (apps) are not installed - that's the whole point. These are executables that need no centralized configuration entry. (IOW, the Registry) They can simply be blown away if no longer needed, or if running from an external source, can merely be ejected, and the machine will have no leftovers.

In order for an application (app) to be truly portable, it cannot use or leave any trace in the registry, including MRU entries.