[SOLVED] firefox vs plasma-workspace

While troubleshooting firefox crashes while loading https://radar.weather.gov, I searched for possible causes in ChangeLog.txt. When plasma-workspace was the dependent variable, I downgraded version 5.27.11.1 to 5.27.11. Firefox loaded the webbage sans kaboom and displayed the map and overlay as advertised. Conclusion: plasma-workspace-5.27.11.1 introduced an error that crashes firefox while loading specific web sites which fail to validate at https://validator.w3.org.