Thunderbird 52.6.1 fails to save exceptions for remote content after program

Thunderbird has suddenly forgotten all of my security exceptions concerning remote content. I went through my inbox, adding each again. Remote content showed correctly for each message until I closed and restarted Thunderbird. Then all exceptions were lost again when I checked. File permissions for my .thunderbird folder have not changed as far as I can tell. This may have occurred several days ago. I had assumed that the content was failing to show because of network problems until I noticed the “content” bar this evening.
I have tried the OSS repo version and also the Tumbleweed Mozilla repo version with identical results. I am also posting this on the Mozilla forum as perhaps it is a new bug.

I’m still experiencing this.

It looks like someone reported it as a bug to openSUSE a few days ago:

I too am experiencing this. Still.

Yes, I read the Thunderbird support page.

Thunderbird 52.8.0 (64-bit). OpenSuse Leap 42.3, KDE Plasma 5.8.7.