Can't import .webm audio with FFmpeg and v2.3.1

I’m running Mac OS 10.14.4 and recently upgraded to Audacity 2.3.1. As part of the upgrade I completely removed the previous version of Audacity and all plugins and support files in directories /Library/Application Support/audacity and ~/Library/Application Support/audacity and I removed the existing Audacity folder in /Applications. Then I installed Audacity v2.3.1, and the latest 64-bit versions of LAME (3.100) and FFmpeg F(55.33.100),C(55.52.102),U(52.66.100). The libraries are showing up correctly in Audacity’s Preferences > Libraries.

Audacity 2.3.1 can no longer seem to import .webm audio. I receive the error, “Audacity did not recognize the type of the file ‘/path/filename.webm’. Try installed FFmpeg. For uncompressed files, also try File > Import > Raw Data.” Importing the raw data doesn’t seem to work, either.

In my previous version of Audacity 2.2.x everything was working correctly.

Are there other codecs and libraries I need to install to successfully import .webm audio?