diff --git a/accessible/base/nsAccessibilityService.cpp b/accessible/base/nsAccessibilityService.cpp
index 2a42c26fd094..f06333814688 100644
--- a/accessible/base/nsAccessibilityService.cpp
+++ b/accessible/base/nsAccessibilityService.cpp
@@ -369,7 +369,11 @@ void nsAccessibilityService::NotifyOfPossibleBoundsChange(
       StaticPrefs::accessibility_cache_enabled_AtStartup()) {
     DocAccessible* document = GetDocAccessible(aPresShell);
     if (document) {
-      LocalAccessible* accessible = document->GetAccessible(aContent);
+      // DocAccessible::GetAccessible() won't return the document if a root
+      // element like body is passed.
+      LocalAccessible* accessible = aContent == document->GetContent()
+                                        ? document
+                                        : document->GetAccessible(aContent);
       if (accessible) {
         document->QueueCacheUpdate(accessible, CacheDomain::Bounds);
       }
@@ -386,7 +390,11 @@ void nsAccessibilityService::NotifyOfComputedStyleChange(
 
   DocAccessible* document = GetDocAccessible(aPresShell);
   if (document) {
-    LocalAccessible* accessible = document->GetAccessible(aContent);
+    // DocAccessible::GetAccessible() won't return the document if a root
+    // element like body is passed.
+    LocalAccessible* accessible = aContent == document->GetContent()
+                                      ? document
+                                      : document->GetAccessible(aContent);
     if (accessible) {
       accessible->MaybeQueueCacheUpdateForStyleChanges();
     }
diff --git a/accessible/tests/browser/bounds/browser_test_iframe_transform.js b/accessible/tests/browser/bounds/browser_test_iframe_transform.js
index d5c810be6eb0..31ad1139f857 100644
--- a/accessible/tests/browser/bounds/browser_test_iframe_transform.js
+++ b/accessible/tests/browser/bounds/browser_test_iframe_transform.js
@@ -140,3 +140,30 @@ addAccessibleTask(
     },
   }
 );
+
+/**
+ * Test document bounds change notifications.
+ * Note: This uses iframes to change the doc container size in order
+ * to have the doc accessible's bounds change.
+ */
+addAccessibleTask(
+  `<div id="div" style="width: 30px; height: 30px"></div>`,
+  async function(browser, accDoc, foo) {
+    const docWidth = () => {
+      let width = {};
+      accDoc.getBounds({}, {}, width, {});
+      return width.value;
+    };
+
+    await untilCacheIs(docWidth, 0, "Doc width is 0");
+    await invokeSetStyleIframe(browser, DEFAULT_IFRAME_ID, "width", `300px`);
+    await untilCacheIs(docWidth, 300, "Doc width is 300");
+  },
+  {
+    chrome: false,
+    topLevel: false,
+    iframe: true,
+    remoteIframe: isCacheEnabled /* works, but timing is tricky with no cache */,
+    iframeAttrs: { style: "width: 0;" },
+  }
+);