diff --git a/toolkit/actors/UserCharacteristicsCanvasRenderingChild.sys.mjs b/toolkit/actors/UserCharacteristicsCanvasRenderingChild.sys.mjs
index a76f5b07f06e..dbb86d8dc5c1 100644
--- a/toolkit/actors/UserCharacteristicsCanvasRenderingChild.sys.mjs
+++ b/toolkit/actors/UserCharacteristicsCanvasRenderingChild.sys.mjs
@@ -52,7 +52,10 @@ export class UserCharacteristicsCanvasRenderingChild extends JSWindowActorChild
           "Error getting canvas debug info during render: ",
           await stringifyError(e)
         );
-        return { error: "COULD_NOT_GET_DEBUG_INFO", originalError: e };
+        return {
+          error: "COULD_NOT_GET_DEBUG_INFO",
+          originalError: await stringifyError(e),
+        };
       }
 
       if (debugInfo.isAccelerated !== isAccelerated) {
@@ -66,10 +69,13 @@ export class UserCharacteristicsCanvasRenderingChild extends JSWindowActorChild
         await recipe.func(this.contentWindow, canvas, ctx);
       } catch (e) {
         lazy.console.error("Error rendering canvas: ", await stringifyError(e));
-        return { error: "RENDERING_ERROR", originalError: e };
+        return {
+          error: "RENDERING_ERROR",
+          originalError: await stringifyError(e),
+        };
       }
 
-      return sha1(canvas.toDataURL("image/png", 1));
+      return sha1(canvas.toDataURL("image/png", 1)).catch(stringifyError);
     };
 
     const data = {
diff --git a/toolkit/actors/UserCharacteristicsWindowInfoChild.sys.mjs b/toolkit/actors/UserCharacteristicsWindowInfoChild.sys.mjs
index b32658c150da..aea0e837f92e 100644
--- a/toolkit/actors/UserCharacteristicsWindowInfoChild.sys.mjs
+++ b/toolkit/actors/UserCharacteristicsWindowInfoChild.sys.mjs
@@ -133,7 +133,7 @@ export class UserCharacteristicsWindowInfoChild extends JSWindowActorChild {
   didDestroy() {
     this.destroyed = true;
     for (const [type, handler] of Object.entries(this.handlers)) {
-      this.contentWindow.windowRoot.removeEventListener(type, handler);
+      this.contentWindow?.windowRoot?.removeEventListener(type, handler);
     }
   }
 
diff --git a/toolkit/components/resistfingerprinting/UserCharacteristicsPageService.sys.mjs b/toolkit/components/resistfingerprinting/UserCharacteristicsPageService.sys.mjs
index 5e95b66a195f..b11428ffe74f 100644
--- a/toolkit/components/resistfingerprinting/UserCharacteristicsPageService.sys.mjs
+++ b/toolkit/components/resistfingerprinting/UserCharacteristicsPageService.sys.mjs
@@ -123,7 +123,9 @@ export class UserCharacteristicsPageService {
       } finally {
         lazy.console.debug("Unregistering actors");
         this.cleanUp();
+        lazy.console.debug("Cleanup done");
         this._backgroundBrowsers.delete(browser);
+        lazy.console.debug("Background browser removed");
       }
     });
   }
@@ -131,6 +133,7 @@ export class UserCharacteristicsPageService {
   cleanUp() {
     ChromeUtils.unregisterWindowActor("UserCharacteristics");
     // unregisterWindowActor doesn't throw if the actor is not registered.
+    // (Do note it console.error's but doesn't throw)
     // We can safely double unregister. We do this to handle the case where
     // the actor was registered but the function it was registered timed out.
     ChromeUtils.unregisterWindowActor("UserCharacteristicsWindowInfo");
@@ -244,10 +247,14 @@ export class UserCharacteristicsPageService {
     for (const win of Services.wm.getEnumerator("navigator:browser")) {
       if (!win.closed) {
         for (const tab of win.gBrowser.tabs) {
-          const actor =
+          const actor = await promiseTry(() =>
             tab.linkedBrowser.browsingContext?.currentWindowGlobal.getActor(
               "UserCharacteristicsWindowInfo"
-            );
+            )
+          ).catch(async e => {
+            lazy.console.error("Error getting actor", e);
+            this.handledErrors.push(await stringifyError(e));
+          });
 
           if (!actor) {
             continue;
@@ -897,3 +904,13 @@ function timeoutPromise(promise, ms) {
     );
   });
 }
+
+function promiseTry(func) {
+  return new Promise((resolve, reject) => {
+    try {
+      resolve(func());
+    } catch (error) {
+      reject(error);
+    }
+  });
+}
diff --git a/toolkit/components/resistfingerprinting/content/usercharacteristics.js b/toolkit/components/resistfingerprinting/content/usercharacteristics.js
index 3a4917511441..0bdd89ece24f 100644
--- a/toolkit/components/resistfingerprinting/content/usercharacteristics.js
+++ b/toolkit/components/resistfingerprinting/content/usercharacteristics.js
@@ -1062,7 +1062,7 @@ async function startPopulating() {
   for (const key in data) {
     try {
       output[key] = await data[key];
-      debug(key, output[key].length);
+      debug(key, output[key] ? output[key].length : "null");
     } catch (e) {
       debug("Promise rejected for", key, "Error:", e);
       errors.push(`${key}: ${await stringifyError(e)}`);