I'm using testing (Buster), I've had Firefox pinned for some time because of this bug, and today I found it was for no good reason -- libnss3 is at 2:3.36.1-1, and Firefox has no problem accessing websites using HTTPS.
As the OP said, there seems to have been a problem only with a specific version of libbss3. The dependency in firefox-esr is not set to this specific version, so the package does work with newer (and some older) versions of libnss3; the only thing the firefox-esr maintainers could possibly do is add a (!= 2:3.33-1) to the dependencies, and since 2:3.33-1 is not the current version on any of the Debian releases and architectures (and seems like never will be), it seems like holding a bug against firefox-esr, with severity "grave", is a bit of an overkill. Thanks, Shai.