Yes and no, it depends on how you look at it. When you connect to the internet, your service provider connects you to a Dynamic Name Server or DNS. Every website is an IP address, but the DNS converts the IP to the actual website domain.

You can find the IP address of a website by going into Command Prompt (Windows) and using tracert (website.com)

Firefox only caches IP addresses for a short time, by default, 60 seconds. As far as I know, the IP address is not saved in the places.sqlite database that stores history and bookmarks (it would not be very efficient for data of such short validity to have to go to disk).