Switching your firefox profile to a firefox fork is super easy peasy squeezy cheesy peas.

You just need to follow the steps for moving your profile in this Firefox support article: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

When you start librewolf or whatever you switch to (librewolf is what I use) it will have everything from Firefox including whatever your last session was (if you save your session) and all of your history and bookmarks and even addons and UI customization etc.