diff --git a/dom/base/test/chrome/test_nsITextInputProcessorCallback_at_changing_default_value_of_textarea.html b/dom/base/test/chrome/test_nsITextInputProcessorCallback_at_changing_default_value_of_textarea.html
index e69c79155dbb..c27ab88ccfc8 100644
--- a/dom/base/test/chrome/test_nsITextInputProcessorCallback_at_changing_default_value_of_textarea.html
+++ b/dom/base/test/chrome/test_nsITextInputProcessorCallback_at_changing_default_value_of_textarea.html
@@ -10,6 +10,10 @@
 
 SimpleTest.waitForExplicitFinish();
 SimpleTest.waitForFocus(async () => {
+  await SpecialPowers.pushPrefEnv({
+    set: [["test.ime_content_observer.assert_invalid_cache", true]],
+  });
+
   const textarea = document.createElement("textarea");
   document.body.appendChild(textarea);
   textarea.focus();
diff --git a/dom/base/test/chrome/window_nsITextInputProcessor.xhtml b/dom/base/test/chrome/window_nsITextInputProcessor.xhtml
index 8536ab758f0d..cee017eb480f 100644
--- a/dom/base/test/chrome/window_nsITextInputProcessor.xhtml
+++ b/dom/base/test/chrome/window_nsITextInputProcessor.xhtml
@@ -4966,6 +4966,10 @@ async function runTextNotificationChangesDuringNoFrame() {
 
 async function runTests()
 {
+  await SpecialPowers.pushPrefEnv({
+    set: [["test.ime_content_observer.assert_invalid_cache", true]],
+  });
+
   textareaInFrame = iframe.contentDocument.getElementById("textarea");
   runBeginInputTransactionMethodTests();
   runReleaseTests();
diff --git a/dom/base/test/test_text_change_notifications_when_inserting_text_containing_line_breaks.html b/dom/base/test/test_text_change_notifications_when_inserting_text_containing_line_breaks.html
index 676fbd5ac046..6d7710fc528b 100644
--- a/dom/base/test/test_text_change_notifications_when_inserting_text_containing_line_breaks.html
+++ b/dom/base/test/test_text_change_notifications_when_inserting_text_containing_line_breaks.html
@@ -9,6 +9,10 @@
 
 SimpleTest.waitForExplicitFinish();
 SimpleTest.waitForFocus(async () => {
+  await SpecialPowers.pushPrefEnv({
+    set: [["test.ime_content_observer.assert_invalid_cache", true]],
+  });
+
   const editingHost = document.querySelector("div[contenteditable]");
   const TIP = SpecialPowers.Cc["@mozilla.org/text-input-processor;1"].createInstance(
     SpecialPowers.Ci.nsITextInputProcessor
diff --git a/dom/events/test/test_text_event_in_content.html b/dom/events/test/test_text_event_in_content.html
index 3d7735edb168..d99d6704faeb 100644
--- a/dom/events/test/test_text_event_in_content.html
+++ b/dom/events/test/test_text_event_in_content.html
@@ -12,7 +12,10 @@
 <div contenteditable id="editor"><p><br></p></div>
 <script>
 SimpleTest.waitForExplicitFinish();
-SimpleTest.waitForFocus(function doTests() {
+SimpleTest.waitForFocus(async function doTests() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["test.ime_content_observer.assert_invalid_cache", true]],
+  });
   for (let editorId of ["input", "textarea", "editor"]) {
     let editor = document.getElementById(editorId);
     editor.focus();
diff --git a/editor/libeditor/crashtests/crashtests.list b/editor/libeditor/crashtests/crashtests.list
index 515d278a1453..64b70aaa8c5e 100644
--- a/editor/libeditor/crashtests/crashtests.list
+++ b/editor/libeditor/crashtests/crashtests.list
@@ -1,3 +1,5 @@
+defaults pref(test.ime_content_observer.assert_invalid_cache,true)
+
 load 336081-1.xhtml
 load 403965-1.xhtml
 load 428489-1.html
diff --git a/editor/libeditor/tests/browser.toml b/editor/libeditor/tests/browser.toml
index ac18b6eefc5b..8972b0d9535d 100644
--- a/editor/libeditor/tests/browser.toml
+++ b/editor/libeditor/tests/browser.toml
@@ -1,4 +1,5 @@
 [DEFAULT]
+prefs = ["test.ime_content_observer.assert_invalid_cache=true"]
 skip-if = ["os == 'android'"]
 
 ["browser_bug527935.js"]
diff --git a/editor/libeditor/tests/chrome.toml b/editor/libeditor/tests/chrome.toml
index a12dd64a763b..8b0a21e0050d 100644
--- a/editor/libeditor/tests/chrome.toml
+++ b/editor/libeditor/tests/chrome.toml
@@ -1,4 +1,5 @@
 [DEFAULT]
+prefs = ["test.ime_content_observer.assert_invalid_cache=true"]
 skip-if = ["os == 'android'"]
 
 ["test_bug489202.xhtml"]
diff --git a/editor/libeditor/tests/mochitest.toml b/editor/libeditor/tests/mochitest.toml
index c8be9126152a..80f854c85705 100644
--- a/editor/libeditor/tests/mochitest.toml
+++ b/editor/libeditor/tests/mochitest.toml
@@ -1,6 +1,7 @@
 [DEFAULT]
 prefs = [
   "apz.zoom-to-focused-input.enabled=false",
+  "test.ime_content_observer.assert_invalid_cache=true",
   "ui.dragThresholdX=4", # Bug 1873142
   "ui.dragThresholdY=4", # Bug 1873142
 ]
diff --git a/testing/web-platform/meta/editing/__dir__.ini b/testing/web-platform/meta/editing/__dir__.ini
new file mode 100644
index 000000000000..71db94d7a2f6
--- /dev/null
+++ b/testing/web-platform/meta/editing/__dir__.ini
@@ -0,0 +1 @@
+prefs: [test.ime_content_observer.assert_invalid_cache:true]
diff --git a/testing/web-platform/meta/input-events/__dir__.ini b/testing/web-platform/meta/input-events/__dir__.ini
index daf68383df9a..d5a6c128d1a8 100644
--- a/testing/web-platform/meta/input-events/__dir__.ini
+++ b/testing/web-platform/meta/input-events/__dir__.ini
@@ -1 +1,2 @@
+prefs: [test.ime_content_observer.assert_invalid_cache:true]
 leak-threshold: [default:51200]
diff --git a/widget/tests/window_composition_text_querycontent.xhtml b/widget/tests/window_composition_text_querycontent.xhtml
index 7d479a49a988..646cea1e8c47 100644
--- a/widget/tests/window_composition_text_querycontent.xhtml
+++ b/widget/tests/window_composition_text_querycontent.xhtml
@@ -10870,7 +10870,10 @@ async function runInputModeTest()
 async function runTest()
 {
   await SpecialPowers.pushPrefEnv({
-    set: [["dom.events.textevent.enabled", true]],
+    set: [
+      ["dom.events.textevent.enabled", true],
+      ["test.ime_content_observer.assert_invalid_cache", true],
+    ],
   });
 
   window.addEventListener("unload", window.arguments[0].SimpleTest.finish, {once: true, capture: true});