I recently got a new computer and I was wondering if I could copy my Firefox folder off this laptop onto an SD card, and install it over the Firefox folder in my new PC, thereby transferring all my bookmarks, add-ons, etc?
Nah, it can’t be that easy, can it?
For bookmarks it certainly is that easy. Not sure about the add-ons. Google ‘transfer firefox bookmarks’ to start. Heck, I think there may even be an option on the drop down bookmark menu in Firefox to export/import bookmarks.
Use firefox backup software, it’s free and will restore everything for you for free.
MozBackup. Still the best.
Cheers. If it all goes pear-shaped, I’m going to blame it on you lot. 
I use “Foxmarks” - it syncs bookmarks among computers.