diff --git a/packages/adblocker-webextension/adblocker.ts b/packages/adblocker-webextension/adblocker.ts
index 067e521be8..7f0095e3c1 100644
--- a/packages/adblocker-webextension/adblocker.ts
+++ b/packages/adblocker-webextension/adblocker.ts
@@ -227,48 +227,20 @@ export class WebExtensionBlocker extends FiltersEngine {
     }
   }
 
-  /**
-   * Deal with request cancellation (`{ cancel: true }`) and redirection (`{ redirectUrl: '...' }`).
-   */
-  private onBeforeRequest = (
-    details: WebRequestBeforeRequestDetails,
-  ): chrome.webRequest.BlockingResponse => {
-    const request = fromWebRequestDetails(details);
-    if (request.isMainFrame()) {
-      this.performHTMLFiltering(request);
-      return {};
+  public handleRuntimeMessage = async (
+    msg: IBackgroundCallback & { action?: string },
+    sender: chrome.runtime.MessageSender,
+  ): Promise<any> => {
+    if (sender.tab === undefined) {
+      throw new Error('required "sender.tab" information is not available');
     }
 
-    const { redirect, match } = this.match(request);
-
-    if (redirect !== undefined) {
-      return { redirectUrl: redirect.dataUrl };
-    } else if (match === true) {
-      return { cancel: true };
+    if (sender.tab.id === undefined) {
+      throw new Error('required "sender.tab.id" information is not available');
     }
 
-    return {};
-  };
-
-  /**
-   *
-   */
-  private onHeadersReceived = (
-    details: WebRequestHeadersReceivedDetails,
-  ): chrome.webRequest.BlockingResponse => {
-    return updateResponseHeadersWithCSP(
-      details,
-      this.getCSPDirectives(fromWebRequestDetails(details)),
-    );
-  };
-
-  private onRuntimeMessage = (
-    msg: IBackgroundCallback & { action?: string },
-    sender: chrome.runtime.MessageSender,
-    sendResponse: (response?: any) => void,
-  ): void => {
-    if (sender.tab === undefined || sender.tab.id === undefined || sender.frameId === undefined) {
-      return;
+    if (sender.frameId === undefined) {
+      throw new Error('required "sender.frameId" information is not available');
     }
 
     // Make sure we only listen to messages coming from our content-script
@@ -306,7 +278,7 @@ export class WebExtensionBlocker extends FiltersEngine {
           return;
         }
 
-        this.injectStylesWebExtension(styles, { tabId: sender.tab.id, allFrames: true });
+        await this.injectStylesWebExtension(styles, { tabId: sender.tab.id, allFrames: true });
       }
 
       // Separately, requests cosmetics which depend on the page it self
@@ -337,7 +309,7 @@ export class WebExtensionBlocker extends FiltersEngine {
           return;
         }
 
-        this.injectStylesWebExtension(styles, { tabId: sender.tab.id, frameId });
+        await this.injectStylesWebExtension(styles, { tabId: sender.tab.id, frameId });
 
         // Inject scripts from content script
         const responseFromBackground: IMessageFromBackground = {
@@ -346,12 +318,56 @@ export class WebExtensionBlocker extends FiltersEngine {
           scripts,
           styles: '',
         };
-        sendResponse(responseFromBackground);
+        return responseFromBackground;
       }
     }
   };
 
-  private injectStylesWebExtension(
+  /**
+   * Deal with request cancellation (`{ cancel: true }`) and redirection (`{ redirectUrl: '...' }`).
+   */
+  private onBeforeRequest = (
+    details: WebRequestBeforeRequestDetails,
+  ): chrome.webRequest.BlockingResponse => {
+    const request = fromWebRequestDetails(details);
+    if (request.isMainFrame()) {
+      this.performHTMLFiltering(request);
+      return {};
+    }
+
+    const { redirect, match } = this.match(request);
+
+    if (redirect !== undefined) {
+      return { redirectUrl: redirect.dataUrl };
+    } else if (match === true) {
+      return { cancel: true };
+    }
+
+    return {};
+  };
+
+  private onHeadersReceived = (
+    details: WebRequestHeadersReceivedDetails,
+  ): chrome.webRequest.BlockingResponse => {
+    return updateResponseHeadersWithCSP(
+      details,
+      this.getCSPDirectives(fromWebRequestDetails(details)),
+    );
+  };
+
+  private onRuntimeMessage = (
+    msg: IBackgroundCallback & { action?: string },
+    sender: chrome.runtime.MessageSender,
+    sendResponse: (response?: any) => void,
+  ): void => {
+    this.handleRuntimeMessage(msg, sender)
+      .then(sendResponse)
+      .catch((ex) => {
+        console.error('Error while handling runtime message:', ex);
+      });
+  };
+
+  private async injectStylesWebExtension(
     styles: string,
     {
       tabId,
@@ -362,13 +378,24 @@ export class WebExtensionBlocker extends FiltersEngine {
       frameId?: number;
       allFrames?: boolean;
     },
-  ): void {
-    if (
-      styles.length > 0 &&
-      typeof chrome !== 'undefined' &&
-      chrome.tabs &&
-      chrome.tabs.insertCSS
-    ) {
+  ): Promise<void> {
+    // Abort if stylesheet is empty.
+    if (styles.length === 0) {
+      return;
+    }
+
+    // Abort if `chrome` global is not accessible.
+    if (typeof chrome === 'undefined') {
+      throw new Error('required "chrome" global object is not accessible');
+    }
+
+    // Abort if `chrome.tabs.insertCSS` is not available.
+    if (chrome.tabs === undefined || chrome.tabs.insertCSS === undefined) {
+      throw new Error('required "chrome.tabs.insertCSS" is not available');
+    }
+
+    // Proceed with stylesheet injection.
+    return new Promise((resolve, reject) => {
       chrome.tabs.insertCSS(
         tabId,
         {
@@ -381,11 +408,13 @@ export class WebExtensionBlocker extends FiltersEngine {
         },
         () => {
           if (chrome.runtime.lastError) {
-            console.error('Error while injecting CSS', chrome.runtime.lastError.message);
+            reject(chrome.runtime.lastError.message);
+          } else {
+            resolve();
           }
         },
       );
-    }
+    });
   }
 }