Oh! Right! I think this is a ripple effect of #1 for me, this is how I see the panel for creation a message: https://i.imgur.com/IBVinx4.png

So Firefox put my account password there automatically, and color coded that, but also did this for Max Access Count. And to be frank I filtered out that field when I was looking for relative option to solve #2 problem.

What about an option to expire the message X hours or days after the first access?

So that if one forgets to save / make-use-of the secret thing, and accidentally reload the browser tab, or power off the computer -- it'll still be there, an hour later. But not a week later.

Or if you share the message with a tech illiterate person, who doesn't realize what "expires after first access" means. Then, instead, you can say to him/her: "After you've read my message, you need to use it within two days, thereafter it disappears automatically". And it won't matter if he or she accidentally reloads the browser tab (with the message in it -- trying to access it for a 2nd time), or leaves for lunch and powers off the computer and wants to continue handling your message, after lunch.

(Could be combined with expiring the message after Y days, without any access.)