Quick update. I have been working on other things, but I kept my Firefox browser up and running. I have just clicked on the clipper icon, and it is working. I have just clipped a Simplified article. That's using the same Firefox browser instance with the same tabs (Financial Times, Bloomberg, and Medium) running -- so no clearing of caches or history or anything like that.
Again, this looks less like a problem on my machine and something on the service side. But it must not be very common, otherwise I imagine you'd be getting many, many more complaints.
I regret that I'm heading into a meeting and will be away from this machine for a while, but I remembered to copy and paste the activity logs from the clipper into the attached file for you.
Horace_NYC activity logs.txt