I don't mind the idea of them having a go at improving it. What I want (and I don't think it's too unusual) is for history and site settings to be remembered when I close the browser, and most cookies + data to be deleted with the exception of a few sites where they're kept. Configuring this has been strangely complicated for a long time. To get it to work, I had to figure out this procedure:

1. Select "delete cookies and site data when firefox is closed"
2. Click on "manage exceptions" to add the exceptions. You'd think we'd be done, but...
3. Scroll down to the "history" section
4. Select both "clear history when firefox closes" and "remember history"
5. Click history -> "settings"
6. Select the chekboxes for cookies + data
7. Unselect boxes for history and site settings

It is with some trepidation that I wait to see whether they will have broken my configuration, made things easier, or made it impossible to set things up this way when Debian stable eventually updates to the new ESR in the next few months.