3) Click the clock to make this permission temporary
This is the thing-a-gig that says "Set all on this page to Temporarily Trusted"?
And doing that does something like it sets "skimresources.com" Temporarily Allowed.
4) Restart Firefox
And on restart, skimresources.com is no longer (Temporarily) Allowed, which is what you want.
And dslreports.com is still set to Custom, as I would expect.
Never really messed with Custom (in the day), but I always assumed that Custom overrode (& retained what you had set) & against any other settings.
And to "revert" Custom, you then needed to (specifically) select some other setting, be it Default, Allowed, Temporarily Allowed or Untrusted.
(Or am I still missing something?)
I did notice some differences based on what & how I went about things, but the whole deal confusing me so I'm not sure now what I did see or what is expected to be seen? Like if you set a Custom permission & then also set another domains permission (like Temporarily Allowed) - in the same dialog (meaning that more then 1 domain needed to show up when you went to the Custom), vs., setting Custom & letting the page refresh (whatever) & then going (again) to the NoScript icon & setting a Temporarily Allow of that same second domain. I believe there was a difference in that respect.
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:220.127.116.11) Gecko/20110420 SeaMonkey/2.0.14 Pinball NoScript FlashGot AdblockPlus
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0 SeaMonkey/2.53.13