LibreWolf Profiles

Not sure what you meant. The profile folder is located in X:\PortableApps\LibreWolfPortable\Data\profile, and you can have multiple profiles by making a copy of X:\PortableApps\LibreWolfPortable and rename it to X:\PortableApps\LibreWolfPortable_Copy_2 or _Copy_3 and so on.

On the other hand, my question is, to migrate from Firefox to LibreWolf, can I simply copy my Firefox profile folder X:\PortableApps\FirefoxPortable\Data\profile to the corresponding location of LibreWolf portable and overwrite its default profile folder X:\PortableApps\LibreWolfPortable\Data\profile? Will there be any issues?

Drazick is referring to the "Second Profile" launcher for Firefox Portable that allows you to have separate profiles without needing full duplicate installs. They can't be run at the same time but save space. I wasn't planning on it since LibreWolf isn't anywhere as near as popular as Firefox.

As for copying Firefox profiles in, I'd say try it. It likely won't work as is, but you can probably remove any LibreWolf specific bits and at least get extensions, bookmarks, etc working. You'll likely need to manually re-enable all extensions.