If you have a Mozilla account, or are okay with creating a temporary one, it's pretty easy to synchronize from Firefox to LibreWolf with it. (LibreWolf requires an extra step to enable the account, but it's trivially easy to find in its settings.)
Saved passwords could ve exported into a file. Not sure how it can be imported into bitwarden.
bookmarks also could be exported.
saved session not sure
Bitwarden supports importing Firefox passwords.
Migrate PWs to bitwarden first.
Then you can use Firefox Sync if you want to sync data between the browsers.
Or just do a one-time bookmarks export and import if you don't want to use sync.
If you go to about:profiles, I'm pretty sure there's a button to open the profile folder. Move all the files and folders from the Firefox profile folder to the Librewolf profile folder and you should have your settings and (I think) extensions in Librewolf now. Not sure about passwords but someone here in the replies said you can just import your Firefox passwords into Bitwarden. Since you want to switch to Bitwarden anyway, you should do that. Saving passwords in the browser isn't very secure anyway.
A place to discuss the news and latest developments on the open-source browser Firefox