MacroIT is flickering on Firefox and its failed edit-mode cleanup fails the rest of AllIT

Symptom

org.xwiki.ckeditor.test.ui.MacroIT sometimes times out on Firefox in CKEditorToolBar.toggleSourceMode(), which waits 10s for an element to disappear when switching to Source to check the result:

org.openqa.selenium.TimeoutException: Expected condition failed: waiting for org.xwiki.test.ui.XWikiWebDriver$$Lambda$1872/... (tried for 10 seconds with 500 milliseconds interval)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilElementDisappears(XWikiWebDriver.java:390)
	at org.xwiki.ckeditor.test.po.CKEditorToolBar.toggleSourceMode(CKEditorToolBar.java:299)
	at org.xwiki.ckeditor.test.ui.AbstractCKEditorIT.assertSourceEquals(AbstractCKEditorIT.java:92)
	at org.xwiki.ckeditor.test.ui.MacroIT.children(MacroIT.java:110)

The failed test leaves CKEditor with unsaved changes, so MacroIT#afterEach cannot leave the edit mode (TestUtils.maybeLeaveEditMode is blocked by the beforeunload dialog). Since AllIT runs all its @Nested ITs in a single browser session, every following test then fails in its setup with:

org.openqa.selenium.UnhandledAlertException: Unexpected beforeunload dialog detected. Performed handler "ignore": This page is asking you to confirm that you want to leave — information you've entered may not be saved.
	at org.xwiki.test.docker.internal.junit5.XWikiDockerExtension.beforeEach(XWikiDockerExtension.java:198)

So one flicker turns into ~17 failures: the remaining MacroIT methods, TableIT#backspaceAfterInsertRow, and class-level failures of NestedSaveIT, NestedImageIT, NestedTextAreaIT, NestedLinkIT, NestedQuickActionsIT, NestedUndoRedoIT, NestedLocalizationIT, NestedFilterIT and NestedMacroIT.

Occurrences (stable-17.10.x, Oracle 19.3.0-se2 / Jetty 12-jdk25 / Filesystem / Firefox 158)

• https://ci.xwiki.org/job/XWiki%20Environment%20Tests/job/xwiki-platform/job/stable-17.10.x/320/ (commit 87df7079518): root failure in MacroIT#children
• https://ci.xwiki.org/job/XWiki%20Environment%20Tests/job/xwiki-platform/job/stable-17.10.x/316/ : root failure in MacroIT#inlineEditMacroInsertedFromOtherMacros, same toggleSourceMode timeout, same cascade

The other environments (Chrome) did not fail.

Local reproduction

MacroIT run 3 times locally on commit 87df7079518 with the same configuration (-Dxwiki.test.ui.database=oracle -Dxwiki.test.ui.databaseTag=19.3.0-se2 -Dxwiki.test.ui.servletEngine=jetty -Dxwiki.test.ui.servletEngineTag=12-jdk25 -Dxwiki.test.ui.browser=firefox -Dxwiki.test.ui.blobStore=filesystem, Firefox 158.0): 21/21 executions passed. So it really is intermittent, not a breakage.

Two things to fix

1. the toggleSourceMode timeout itself on Firefox;
2. the missing recovery in the cleanup: a failure that leaves unsaved content should not take down the rest of AllIT (see XWIKI-24806 for the same problem in TextAreaImageUploadIT).