Is it possible to copy a Firefox Portable profile to installed Firefox?

short answer = yes

longer answer = yes, but I don't think I can give instructions well enough, but I will try

I've used a program called MozBackup to copy(backup) Portable Firefox's profile in the past so you can try that (and restore the backup to the installed Firefox), and there is a way of doing it manually.

hmmm ... after a quick google search it appears this question has been asked before:

here--> https://portableapps.com/node/35693

>and apparently I've even commented there 0.o
>It would off been nice to remember commenting
>I definitely need a memory upgrade

I did recommend in that thread MozBackup (with links for downloading and information) and someone else recommended FEBE ... Firefox Extension Backup Extension.

The following link explains how to copy the profile from an installed Firefox to a portable one, so reverse the instructions should work.

https://portableapps.com/support/firefox_portable#local_profile

I think the reversed order is:

--> copy the FirefoxPortable\Data\profile directory
--> to C:\Documents and Settings\[user]\Application Data\Mozilla\Firefox\Profiles\default.???\

or wherever the installed version of Firefox has put it's Profiles folder

Good Luck