I don’t actually care about the IP address, I am just curious if a website is accessed via IPv4 or IPv6.

Firefox (I am not going to repeat the obvious ones that have been mentioned numerous times):

• IPvFoo: Display IP address information for website
• tabdetach: I always juggle around my windows. Being able to detach, attach and merge tabs without using the mouse is really useful.
• Cookie AutoDelete: Removes cookies unless whitelisted

i.redd.it and v.redd.it might make sense as well. There is a bunch of subdomains and other domains (…oauth.reddit.com, …redditmedia.com, …), but they are only used if you connect the the main sites (i. e., not hot-linked), so blocking those will be sufficient to block all reddit-traffic.