Firefox bookmarks are stored in the places.sqlite file in the Profile folder.

https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

I cannot open places.sqlite without an App from the store?? Is this something that changed with Windows 10??? No more "Favorites" Folder???

Why would you want to "open" the places.sqlite file? It's not really human readable.

No, not a change with Windows 10, although if your not using IE and using Edge the Favorites folder may never have been created. Whatever, nothing to do with Firefox.

Firefox has never used the "Favorites" folder. Prior to using places.sqlite starting with Firefox 3.0 in June 2008, Firefox used a file named bookmarks.html. AFAIK, Internet Explorer (and its clones/skins) was the only web browser to use the Favorites folder in Windows. The one exception being an extension called PlainOldFavorites that would display the IE Favorites inside Firefox

Hi   !
Maybe you'll find this helpful:
For   Internet Explorer:
https://www.winhelp.us/internet-explorer-11-favorites.html
For   Edge:
www.ghacks.net/2016/08/24/favorites-microsoft-edge/