Safari on macOS shows the URLs in activity, here's an example with Roblox.com opened in Safari:
Here are some Firefox processes listed in task manager, they don't show URLs.
I'm not 100% sure how Firefox handles each tab with process, like whether each tab has its own process or whatnot, but I think it would be very useful for each process to name URLs / tabs its handling to get an idea of how many system resources its using, even if it's not precise. Since I use my browser the most on macOS, it tends to use the most resources by far.