EDIT

I don't remember in which situation this happened, but I had this exception two times today during the tutorial session, when I was presenting the taxeditor via jitsi screen sharing in Firefox:

!ENTRY org.eclipse.ui 4 0 2020-05-15 15:39:30.089
!MESSAGE This is an unexpected error.
Please contact EDIT Support (EditSupport@bgbm.org) with the error trace below (click on the 'Details' button).
!STACK 0
java.lang.Exception: last remote method : https://api.cybertaxonomy.org:443/casearia/remoting/term.service
last remote request client time : 2020-05-15T15:39:27.949
last remote request response header time : Fri, 15 May 2020 15:39:28 GMT
client error time : 2020-05-15T15:39:28.31
login : admin
editor version : 5.14.0
server : api.cybertaxonomy.org (cybertaxonomy.org) / casearia
schema version : 5.12.0.0.20191202
os : Linux 5.3.0-51-generic amd64
java : 1.8.0_131
org.eclipse.swt.SWTException: Failed to execute runnable (org.eclipse.swt.SWTError: No more handles [Unknown Mozilla path (MOZILLA_FIVE_HOME not set)])
        at org.eclipse.swt.SWT.error(SWT.java:4533)
        at org.eclipse.swt.SWT.error(SWT.java:4448)
        at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:185)
        at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4536)
        at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4154)
        at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)
        at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
        at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)
        at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)
        at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:693)
        at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
        at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:610)
        at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
        at eu.etaxonomy.taxeditor.Application.start(Application.java:24)
        at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:673)
        at org.eclipse.equinox.launcher.Main.basicRun(Main.java:610)
        at org.eclipse.equinox.launcher.Main.run(Main.java:1519)
        at org.eclipse.equinox.launcher.Main.main(Main.java:1492)
Caused by: org.eclipse.swt.SWTError: No more handles [Unknown Mozilla path (MOZILLA_FIVE_HOME not set)]
        at org.eclipse.swt.SWT.error(SWT.java:4559)
        at org.eclipse.swt.browser.Mozilla.initMozilla(Mozilla.java:2237)
        at org.eclipse.swt.browser.Mozilla.create(Mozilla.java:691)
        at org.eclipse.swt.browser.Browser.<init>(Browser.java:99)
        at eu.etaxonomy.taxeditor.ui.element.BrowserElement.<init>(BrowserElement.java:41)
        at eu.etaxonomy.taxeditor.ui.element.CdmFormFactory.createBrowserElement(CdmFormFactory.java:1093)
        at eu.etaxonomy.taxeditor.ui.section.feature.FeatureDistributionDetailElement.createControls(FeatureDistributionDetailElement.java:67)
        at eu.etaxonomy.taxeditor.ui.section.feature.FeatureDistributionDetailElement.createControls(FeatureDistributionDetailElement.java:1)
        at eu.etaxonomy.taxeditor.ui.section.AbstractCdmDetailElement.updateContent(AbstractCdmDetailElement.java:107)
        at eu.etaxonomy.taxeditor.ui.section.AbstractCdmDetailElement.setEntity(AbstractCdmDetailElement.java:94)
        at eu.etaxonomy.taxeditor.ui.section.AbstractCdmDetailSection.setEntity(AbstractCdmDetailSection.java:145)
        at eu.etaxonomy.taxeditor.view.detail.CdmSectionPart.setFormInput(CdmSectionPart.java:167)
        at org.eclipse.ui.forms.ManagedForm.setInput(ManagedForm.java:210)
        at eu.etaxonomy.taxeditor.view.e4.AbstractCdmDataViewerE4.refresh(AbstractCdmDataViewerE4.java:162)
        at eu.etaxonomy.taxeditor.view.e4.AbstractCdmDataViewerE4.setInput(AbstractCdmDataViewerE4.java:143)
        at eu.etaxonomy.taxeditor.view.e4.details.DetailsViewerE4.setInput(DetailsViewerE4.java:202)
        at eu.etaxonomy.taxeditor.view.e4.details.DetailsViewerE4.setInput(DetailsViewerE4.java:173)
        at eu.etaxonomy.taxeditor.view.e4.AbstractCdmEditorPartE4.showViewer(AbstractCdmEditorPartE4.java:284)
        at eu.etaxonomy.taxeditor.view.e4.details.DetailsPartE4.selectionChanged_internal(DetailsPartE4.java:107)
        at eu.etaxonomy.taxeditor.view.e4.AbstractCdmEditorPartE4$DelaySelection.run(AbstractCdmEditorPartE4.java:94)
        at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
        at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:182)
        ... 24 more

        at eu.etaxonomy.taxeditor.model.MessagingUtils$1.run(MessagingUtils.java:304)
        at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
        at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:182)
        at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4536)
        at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4154)
        at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)
        at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
        at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)
        at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)
        at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:693)
        at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
        at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:610)
        at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
        at eu.etaxonomy.taxeditor.Application.start(Application.java:24)
        at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
        at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
        at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:673)
        at org.eclipse.equinox.launcher.Main.basicRun(Main.java:610)
        at org.eclipse.equinox.launcher.Main.run(Main.java:1519)
        at org.eclipse.equinox.launcher.Main.main(Main.java:1492)