--- a/devtools/client/debugger/test/mochitest/browser_dbg-breaking.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-breaking.js
@@ -18,23 +18,33 @@ add_task(async function() {
   await addBreakpoint(dbg, "scripts.html", 21);
 
   reload(dbg);
 
   await waitForDispatch(dbg.store, "NAVIGATE");
   await waitForSelectedSource(dbg, "doc-scripts.html");
   await waitForPaused(dbg);
 
+  let whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, "Paused on breakpoint");
+
   assertPausedLocation(dbg);
   await resume(dbg);
 
   info("Create an eval script that pauses itself.");
   invokeInTab("doEval");
   await waitForPaused(dbg);
 
+  whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, "Paused on debugger statement");
+
   await resume(dbg);
   const source = getSelectedSource();
   ok(!source.url, "It is an eval source");
 
   await addBreakpoint(dbg, source, 5);
   invokeInTab("evaledFunc");
   await waitForPaused(dbg);
   assertPausedLocation(dbg);

--- a/devtools/client/debugger/test/mochitest/browser_dbg-dom-mutation-breakpoints.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-dom-mutation-breakpoints.js
@@ -16,17 +16,16 @@ const DMB_TEST_URL =
   "https://example.com/browser/devtools/client/debugger/test/mochitest/examples/doc-dom-mutation.html";
 
 async function enableMutationBreakpoints() {
   await pushPref("devtools.debugger.features.dom-mutation-breakpoints", true);
   await pushPref("devtools.markup.mutationBreakpoints.enabled", true);
   await pushPref("devtools.debugger.dom-mutation-breakpoints-visible", true);
 }
 
-
 add_task(async function() {
   // Enable features
   await enableMutationBreakpoints();
   info("Switches over to the inspector pane");
 
   const { inspector, toolbox } = await openInspectorForURL(DMB_TEST_URL);
 
   info("Selecting the body node");
@@ -63,30 +62,61 @@ add_task(async function() {
   checkbox.click();
   await waitFor(() => checkbox.checked);
 
   info("Changing attribute to trigger debugger pause");
   SpecialPowers.spawn(gBrowser.selectedBrowser, [], function() {
     content.document.querySelector("#attribute").click();
   });
   await waitForPaused(dbg);
+  let whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(
+    whyPaused,
+    `Paused on DOM mutation\nDOM Mutation: 'attributeModified'\nbody`
+  );
+
   await resume(dbg);
 
   info("Changing style to trigger debugger pause");
   SpecialPowers.spawn(gBrowser.selectedBrowser, [], function() {
     content.document.querySelector("#style-attribute").click();
   });
   await waitForPaused(dbg);
   await resume(dbg);
 
-  info("Changing subtree to trigger debugger pause");
+  info("Adding element in subtree to trigger debugger pause");
   SpecialPowers.spawn(gBrowser.selectedBrowser, [], function() {
-    content.document.querySelector("#subtree").click();
+    content.document.querySelector("#add-in-subtree").click();
   });
   await waitForPaused(dbg);
+  whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(
+    whyPaused,
+    `Paused on DOM mutation\nDOM Mutation: 'subtreeModified'\nbodyAdded:div`
+  );
+
+  await resume(dbg);
+
+  info("Removing element in subtree to trigger debugger pause");
+  SpecialPowers.spawn(gBrowser.selectedBrowser, [], function() {
+    content.document.querySelector("#remove-in-subtree").click();
+  });
+  await waitForPaused(dbg);
+  whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(
+    whyPaused,
+    `Paused on DOM mutation\nDOM Mutation: 'subtreeModified'\nbodyRemoved:div`
+  );
+
   await resume(dbg);
 
   info("Blackboxing the source prevents debugger pause");
   await waitForSource(dbg, "dom-mutation.original.js");
 
   const source = findSource(dbg, "dom-mutation.original.js");
 
   await selectSource(dbg, source);
@@ -102,10 +132,9 @@ add_task(async function() {
 
   await selectSource(dbg, source);
   await clickElement(dbg, "blackbox");
   await waitForDispatch(dbg.store, "BLACKBOX");
 
   info("Removing breakpoints works");
   dbg.win.document.querySelector(".dom-mutation-list .close-btn").click();
   await waitForAllElements(dbg, "domMutationItem", 1, true);
-
 });

--- a/devtools/client/debugger/test/mochitest/browser_dbg-event-breakpoints.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-event-breakpoints.js
@@ -23,16 +23,22 @@ add_task(async function() {
     "timer.timeout.set",
     "timer.timeout.fire",
     "script.source.firstStatement",
   ]);
 
   invokeInTab("clickHandler");
   await waitForPaused(dbg);
   assertPauseLocation(dbg, 12);
+
+  const whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, `Paused on event breakpoint\nDOM 'click' event`);
+
   await resume(dbg);
 
   invokeInTab("xhrHandler");
   await waitForPaused(dbg);
   assertPauseLocation(dbg, 20);
   await resume(dbg);
 
   invokeInTab("timerHandler");
@@ -85,12 +91,16 @@ function assertPauseLocation(dbg, line, 
   is(location.sourceId, source.id, `correct sourceId`);
   is(location.line, line, `correct line`);
 
   assertPausedLocation(dbg);
 }
 
 async function invokeOnElement(selector, action) {
   await SpecialPowers.focus(gBrowser.selectedBrowser);
-  await SpecialPowers.spawn(gBrowser.selectedBrowser, [selector, action], (_selector, _action) => {
-    content.document.querySelector(_selector)[_action]();
-  });
+  await SpecialPowers.spawn(
+    gBrowser.selectedBrowser,
+    [selector, action],
+    (_selector, _action) => {
+      content.document.querySelector(_selector)[_action]();
+    }
+  );
 }

--- a/devtools/client/debugger/test/mochitest/browser_dbg-pause-exceptions.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-pause-exceptions.js
@@ -17,16 +17,22 @@ add_task(async function() {
   await uncaughtException();
   ok(!isPaused(dbg));
 
   log("2. Test pausing on an uncaught exception");
   await togglePauseOnExceptions(dbg, true, true);
   uncaughtException();
   await waitForPaused(dbg);
   assertPausedLocation(dbg);
+
+  const whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, `Paused on exception\nunreachable`);
+
   await resume(dbg);
 
   log("2.b Test throwing the same uncaught exception pauses again");
   await togglePauseOnExceptions(dbg, true, true);
   uncaughtException();
   await waitForPaused(dbg);
   assertPausedLocation(dbg);
   await resume(dbg);

--- a/devtools/client/debugger/test/mochitest/browser_dbg-stepping.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-stepping.js
@@ -6,16 +6,22 @@
 requestLongerTimeout(5);
 
 add_task(async function test() {
   const dbg = await initDebugger("big-sourcemap.html", "big-sourcemap");
   invokeInTab("hitDebugStatement");
   await waitForPaused(dbg, "bundle.js");
 
   await stepIn(dbg);
+
+  const whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, `Paused while stepping`);
+
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);
   await stepIn(dbg);

--- a/devtools/client/debugger/test/mochitest/browser_dbg-watchpoints.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-watchpoints.js
@@ -28,16 +28,20 @@ add_task(async function() {
   await addedWatchpoint;
   popup.hidePopup();
 
   await resume(dbg);
   await waitForPaused(dbg);
   await waitForState(dbg, () => dbg.selectors.getSelectedInlinePreviews());
   assertPausedAtSourceAndLine(dbg, sourceId, 17);
   is(await getScopeValue(dbg, 5), "3");
+  const whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, `Paused on property get\nobj.b`);
 
   info("Resume and wait to pause at the access to b in the first `obj.b;`");
   await resume(dbg);
   await waitForPaused(dbg);
   assertPausedAtSourceAndLine(dbg, sourceId, 19);
 
   info("Remove the get watchpoint on b");
   const removedWatchpoint1 = waitForDispatch(dbg.store, "REMOVE_WATCHPOINT");

--- a/devtools/client/debugger/test/mochitest/browser_dbg-xhr-breakpoints.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-xhr-breakpoints.js
@@ -7,33 +7,39 @@ add_task(async function() {
 
   const dbg = await initDebugger("doc-xhr.html", "fetch.js");
 
   await addXHRBreakpoint(dbg, "doc", "GET");
 
   await SpecialPowers.spawn(
     gBrowser.selectedBrowser,
     [EXAMPLE_REMOTE_URL + "doc-early-xhr.html"],
-    (remoteUrl) => {
+    remoteUrl => {
       const firstIframe = content.document.createElement("iframe");
       content.document.body.append(firstIframe);
       firstIframe.src = remoteUrl;
     }
   );
 
   await waitForPaused(dbg);
   assertPausedLocation(dbg);
+
+  const whyPaused = await waitFor(
+    () => dbg.win.document.querySelector(".why-paused")?.innerText
+  );
+  is(whyPaused, `Paused on XMLHttpRequest`);
+
   await resume(dbg);
 
   await dbg.actions.removeXHRBreakpoint(0);
 
   await SpecialPowers.spawn(
     gBrowser.selectedBrowser,
     [EXAMPLE_REMOTE_URL + "doc-early-xhr.html"],
-    (remoteUrl) => {
+    remoteUrl => {
       const secondIframe = content.document.createElement("iframe");
       content.document.body.append(secondIframe);
       secondIframe.src = remoteUrl;
     }
   );
 
   // Wait for some time, in order to wait for it to be paused
   // in case we regress
@@ -53,17 +59,16 @@ add_task(async function() {
   await waitForPaused(dbg);
   assertPausedLocation(dbg);
   await resume(dbg);
 
   await dbg.actions.removeXHRBreakpoint(0);
   await invokeInTab("main", "doc-xhr.html");
   assertNotPaused(dbg);
 
-
   info("Test that we do not pause on different method type");
   await addXHRBreakpoint(dbg, "doc", "POST");
   await invokeInTab("main", "doc-xhr.html");
   assertNotPaused(dbg);
 });
 
 // Tests the "pause on any URL" checkbox works properly
 add_task(async function() {
@@ -152,17 +157,19 @@ async function removeXHRBreakpoint(dbg, 
     closeButtons[index].click();
   }
 
   await waitForDispatch(dbg.store, "REMOVE_XHR_BREAKPOINT");
 }
 
 function getXHRBreakpointsElements(dbg) {
   return [
-    ...dbg.win.document.querySelectorAll(".xhr-breakpoints-pane .xhr-container")
+    ...dbg.win.document.querySelectorAll(
+      ".xhr-breakpoints-pane .xhr-container"
+    ),
   ];
 }
 
 function getXHRBreakpointLabels(elements) {
   return elements.map(element => element.title);
 }
 
 function getXHRBreakpointCheckbox(dbg) {

--- a/devtools/client/debugger/test/mochitest/examples/doc-dom-mutation.html
+++ b/devtools/client/debugger/test/mochitest/examples/doc-dom-mutation.html
@@ -6,13 +6,14 @@
   <head>
     <meta charset="utf-8"/>
     <title>Debugger test page</title>
   </head>
 
   <body>
     <button title="Hello" id="attribute" onclick="changeAttribute()">Click me!</button>
     <button id="style-attribute" onclick="changeStyleAttribute()">Click me!</button>
-    <button id="subtree" onclick="changeSubtree()">Click me!</button>
+    <button id="add-in-subtree" onclick="addDivToBody()">add div to body</button>
+    <button id="remove-in-subtree" onclick="removeDivInBody()">remove div in body</button>
     <button id="blackbox" onclick="changeAttribute();&#xA;debugger;&#xA;//# sourceURL=click.js">Click me!</button>
     <script src="dom-mutation.js"></script>
   </body>
 </html>

--- a/devtools/client/debugger/test/mochitest/examples/dom-mutation.js
+++ b/devtools/client/debugger/test/mochitest/examples/dom-mutation.js
@@ -2,12 +2,17 @@ function changeAttribute() {
   const title = document.body.title === "Goodbye" ? "Hello" : "Goodbye";
   document.body.setAttribute("title", title);
 }
 
 function changeStyleAttribute() {
   document.body.style.color = "blue";
 }
 
-function changeSubtree() {
+function addDivToBody() {
   document.body.appendChild(document.createElement("div"));
 }
+
+function removeDivInBody() {
+  document.body.querySelector("div").remove();
+}
+
 //# sourceMappingURL=dom-mutation.js.map