I just went through a long list of keyboard shortcuts for Firefox. One that I didn’t see that I would find useful is to press something like ⇧ Shift + ⌘ + C to copy the URL and then paste it into an email or message to send to someone. Does something like this exist?
Personally I just use Ctrl+L to quickly access to the URL Bar and then use Ctrl+C, I know is not exactly what you are searching but it works for me.