cisco webex with openjdk - no audio

On slackware-current (kernel 5.4.48) using the slackware version 78 of firefox and alienBob's version of openjdk(8u252_b09) and icedtea-web, I am able to join Cisco WebEx meetings, but there is no audio. I have loaded the recent (06/2020) Cisco Firefox Web Extension, so the meeting comes up in the Firefox browser, not the Cisco desktop app (which appears to be a 32 bit binary, from ?stale? posts). I have multilib installed. Much of the WebEx info online is stale, so it is hard to tell what to try next. The Cisco WebEx test site cannot be used since it says "browser, browser version or O/S not supported" and does not allow attempting to join a test meeting. I CAN join a test meeting put up by Cisco Tech Support (thanks, Cisco), but they cannot offer further tests or help once I was able to join their meeting. I checked that a Java audio player works, and plays thru PulseAudio without problems. icetea-sound is not required for that. Do I need icedtea-sound for WebEx? I notice that alienBob's openjdk does not include a .../jvm/ directory. Is this an issue?

I see no signs of a java plugin for Firefox in their addons search results. Is this an issue? Is there a way to use the browser to play test audio through java?

Etc.

Need a java/firefox/webex guru to help with understanding this...
P.S. Zoom works fine, but I need to take webinars offered only thru WebEx! I could switch to Oracle JDK, (sigh), but I have no way to test that either...

I'm willing to learn java and write a plugin for this (retired software developer), but need some "bootstrap" pointers!