diff --git a/modules/zen/ZenWindowSync.sys.mjs b/modules/zen/ZenWindowSync.sys.mjs
index 8daa5b3..33474a5 100644
--- a/modules/zen/ZenWindowSync.sys.mjs
+++ b/modules/zen/ZenWindowSync.sys.mjs
@@ -781 +781 @@ class nsZenWindowSync {
-        return;
+        return false;
@@ -785 +785 @@ class nsZenWindowSync {
-        return;
+        return false;
@@ -787 +787 @@ class nsZenWindowSync {
-      await this.#styleSwapedBrowsers(aOurTab, aOtherTab, () => {
+      return this.#styleSwapedBrowsers(aOurTab, aOtherTab, () => {
@@ -789 +789 @@ class nsZenWindowSync {
-          this.#swapBrowserDocShellsInner(aOurTab, aOtherTab);
+          return this.#swapBrowserDocShellsInner(aOurTab, aOtherTab);
@@ -794,0 +795 @@ class nsZenWindowSync {
+          return false;
@@ -829,7 +830,8 @@ class nsZenWindowSync {
-      tabListener = new otherTabBrowser.zenTabProgressListener(
-        aTab,
-        otherBrowser,
-        true,
-        false
-      );
-      otherTabBrowser.zenSetTabProgressListener(aTab, tabListener);
+      try {
+        tabListener = new otherTabBrowser.zenTabProgressListener(
+          aTab,
+          otherBrowser,
+          true,
+          false
+        );
+        otherTabBrowser.zenSetTabProgressListener(aTab, tabListener);
@@ -837,3 +839,6 @@ class nsZenWindowSync {
-      const notifyAll = Ci.nsIWebProgress.NOTIFY_ALL;
-      filter.addProgressListener(tabListener, notifyAll);
-      otherBrowser.webProgress.addProgressListener(filter, notifyAll);
+        const notifyAll = Ci.nsIWebProgress.NOTIFY_ALL;
+        filter.addProgressListener(tabListener, notifyAll);
+        otherBrowser.webProgress.addProgressListener(filter, notifyAll);
+      } catch (e) {
+        console.error(`Error restoring tab progress listener:`, e);
+      }
@@ -899 +904 @@ class nsZenWindowSync {
-      return;
+      return false;
@@ -903,0 +909 @@ class nsZenWindowSync {
+    let didSwap = false;
@@ -913,0 +920 @@ class nsZenWindowSync {
+          didSwap = true;
@@ -918,0 +926 @@ class nsZenWindowSync {
+          return;
@@ -962,0 +971,3 @@ class nsZenWindowSync {
+    if (!didSwap) {
+      return false;
+    }
@@ -972,9 +983,13 @@ class nsZenWindowSync {
-    for (let attr of kAttributesToRemove) {
-      aOtherTab.removeAttribute(attr);
-    }
-    if (focus) {
-      // Recalculate the focus in order to allow the user to continue typing
-      // inside the web content area without having to click outside and back in.
-      aOurTab.linkedBrowser.blur();
-      aOurTab.documentGlobal.gBrowser._adjustFocusAfterTabSwitch(aOurTab);
-      aOurTab.linkedBrowser.docShellIsActive = true;
+    try {
+      for (let attr of kAttributesToRemove) {
+        aOtherTab.removeAttribute(attr);
+      }
+      if (focus) {
+        // Recalculate the focus in order to allow the user to continue typing
+        // inside the web content area without having to click outside and back in.
+        aOurTab.linkedBrowser.blur();
+        aOurTab.documentGlobal.gBrowser._adjustFocusAfterTabSwitch(aOurTab);
+        aOurTab.linkedBrowser.docShellIsActive = true;
+      }
+    } catch (e) {
+      console.error(`Error cleaning up browser after docshell swap:`, e);
@@ -981,0 +997 @@ class nsZenWindowSync {
+    return true;
@@ -997,7 +1013,17 @@ class nsZenWindowSync {
-        const browserBlob =
-          await aOtherTab.documentGlobal.PageThumbs.captureToBlob(
-            aOtherTab.linkedBrowser,
-            {
-              fullScale: true,
-              fullViewport: true,
-              backgroundColor: "transparent",
+        let mySrc = "";
+        try {
+          const browserBlob =
+            await aOtherTab.documentGlobal.PageThumbs.captureToBlob(
+              aOtherTab.linkedBrowser,
+              {
+                fullScale: true,
+                fullViewport: true,
+                backgroundColor: "transparent",
+              }
+            );
+
+          mySrc = await new Promise(r => {
+            const reader = new FileReader();
+            if (!browserBlob) {
+              r("");
+              return;
@@ -1005,17 +1031,9 @@ class nsZenWindowSync {
-          );
-
-        let mySrc = await new Promise(r => {
-          const reader = new FileReader();
-          if (!browserBlob) {
-            r("");
-            return;
-          }
-          reader.readAsDataURL(browserBlob);
-          reader.onloadend = function () {
-            // result includes identifier 'data:image/png;base64,' plus the base64 data
-            r(reader.result);
-          };
-          reader.onerror = function () {
-            r("");
-          };
-        });
+            reader.readAsDataURL(browserBlob);
+            reader.onloadend = function () {
+              // result includes identifier 'data:image/png;base64,' plus the base64 data
+              r(reader.result);
+            };
+            reader.onerror = function () {
+              r("");
+            };
+          });
@@ -1023,2 +1041,7 @@ class nsZenWindowSync {
-        await this.#createPseudoImageForBrowser(otherBrowser, mySrc);
-        callback();
+          await this.#createPseudoImageForBrowser(otherBrowser, mySrc);
+        } catch (e) {
+          // The thumbnail only hides the visual transition. It must not block
+          // the docshell transfer or leave the global swap queue pending.
+          console.error(`Error preparing docshell swap styling:`, e);
+        }
+        const didSwap = callback();
@@ -1026,5 +1049,10 @@ class nsZenWindowSync {
-          otherBrowser.setAttribute("zen-pseudo-hidden", "true");
-          ourBrowser.removeAttribute("zen-pseudo-hidden");
-          this.#maybeRemovePseudoImageForBrowser(ourBrowser);
-          ourBrowser.focus();
-          resolve();
+          try {
+            otherBrowser.setAttribute("zen-pseudo-hidden", "true");
+            ourBrowser.removeAttribute("zen-pseudo-hidden");
+            this.#maybeRemovePseudoImageForBrowser(ourBrowser);
+            ourBrowser.focus();
+          } catch (e) {
+            console.error(`Error cleaning up docshell swap styling:`, e);
+          } finally {
+            resolve(didSwap);
+          }
@@ -1126 +1153,0 @@ class nsZenWindowSync {
-        targetTab._zenContentsVisible = true;
@@ -1130 +1157 @@ class nsZenWindowSync {
-        delete tab._zenContentsVisible;
+        let didSwap = false;
@@ -1132 +1159 @@ class nsZenWindowSync {
-          this.#swapBrowserDocShellsInner(targetTab, tab, {
+          didSwap = this.#swapBrowserDocShellsInner(targetTab, tab, {
@@ -1141,0 +1169,5 @@ class nsZenWindowSync {
+        if (!didSwap) {
+          continue;
+        }
+        targetTab._zenContentsVisible = true;
+        delete tab._zenContentsVisible;
@@ -1186,3 +1218,8 @@ class nsZenWindowSync {
-          otherTabToShow._zenContentsVisible = true;
-          delete tab._zenContentsVisible;
-          await this.#swapBrowserDocShellsAsync(otherTabToShow, tab);
+          const didSwap = await this.#swapBrowserDocShellsAsync(
+            otherTabToShow,
+            tab
+          );
+          if (didSwap) {
+            otherTabToShow._zenContentsVisible = true;
+            delete tab._zenContentsVisible;
+          }
@@ -1204 +1240,0 @@ class nsZenWindowSync {
-      selectedTab._zenContentsVisible = true;
@@ -1206 +1241,0 @@ class nsZenWindowSync {
-        delete otherSelectedTab._zenContentsVisible;
@@ -1208 +1243,8 @@ class nsZenWindowSync {
-          this.#swapBrowserDocShellsAsync(selectedTab, otherSelectedTab)
+          this.#swapBrowserDocShellsAsync(selectedTab, otherSelectedTab).then(
+            didSwap => {
+              if (didSwap) {
+                selectedTab._zenContentsVisible = true;
+                delete otherSelectedTab._zenContentsVisible;
+              }
+            }
+          )
@@ -1209,0 +1252,2 @@ class nsZenWindowSync {
+      } else {
+        selectedTab._zenContentsVisible = true;