Firefox as of v 148 (actually a bit earlier than that, but that's what I'm on right now) frequently decides not to load pages anymore. You enter a URL or click on a link and get the status message "Waiting for [URL]..." and you can wait as long as you care to.
When this begins, your only choice is to restart Firefox.
Here is a list of "solutions" to the problem from around the web, which I have tried and found do not fix the problem:
• Turning off DNS-over-HTTPS in Firefox Settings
• Flushing MacOS's DNS cache.
• Going to about:networking and clearing Firefox's DNS cache
• Going into about:config and changing network.dns.disableIPv6 from false to true
• Opening in "troubleshooting mode" or disabling all extensions
• Turning VPN off
• Turning VPN on
