Mind that BroadcastChannel contructor can throw in Firefox

BroadcastChannel constructor throws in Firefox when Enhanced
Tracking Protection is set to "strict".

This behavior could cause scriptlet injection to wholly break
when uBO's logger was opened, as BroadcastChannel() is used
by scriptlets to report information to the logger.

This commit ensures that exceptions from BroadcastChannel
constructor are properly handled.

The scriptlets will fall back to report at the console should
they be unable to report to the logger through BroadcastChannel.

assets/resources/scriptlets.js

@@ -173,13 +173,11 @@ function safeSelf() {
     scriptletGlobals.safeSelf = safe;
     if ( scriptletGlobals.bcSecret === undefined ) { return safe; }
     // This is executed only when the logger is opened
-    const bc = new self.BroadcastChannel(scriptletGlobals.bcSecret);
-    let bcBuffer = [];
     safe.logLevel = scriptletGlobals.logLevel || 1;
     let lastLogType = '';
     let lastLogText = '';
     let lastLogTime = 0;
-    safe.sendToLogger = (type, ...args) => {
+    safe.toLogText = (type, ...args) => {
         if ( args.length === 0 ) { return; }
         const text = `[${document.location.hostname || document.location.href}]${args.join(' ')}`;
         if ( text === lastLogText && type === lastLogType ) {
@@ -188,6 +186,14 @@ function safeSelf() {
         lastLogType = type;
         lastLogText = text;
         lastLogTime = Date.now();
+        return text;
+    };
+    try {
+        const bc = new self.BroadcastChannel(scriptletGlobals.bcSecret);
+        let bcBuffer = [];
+        safe.sendToLogger = (type, ...args) => {
+            const text = safe.toLogText(type, ...args);
+            if ( text === undefined ) { return; }
             if ( bcBuffer === undefined ) {
                 return bc.postMessage({ what: 'messageToLogger', type, text });
             }
@@ -212,6 +218,13 @@ function safeSelf() {
             }
         };
         bc.postMessage('areyouready?');
+    } catch(_) {
+        safe.sendToLogger = (type, ...args) => {
+            const text = safe.toLogText(type, ...args);
+            if ( text === undefined ) { return; }
+            console.log(`uBO${text}`);
+        };
+    }
     return safe;
 }
 
@@ -5144,7 +5157,6 @@ function trustedPreventXhr(...args) {
 }
 
 /**
- * 
  * @trustedScriptlet trusted-prevent-dom-bypass
  * 
  * @description
@@ -5219,7 +5231,6 @@ function trustedPreventDomBypass(
 }
 
 /**
- * 
  * @trustedScriptlet trusted-override-element-method
  * 
  * @description

src/js/scriptlet-filtering.js

@@ -176,6 +176,7 @@ const onScriptletMessageInjector = (( ) => {
         '(',
         function(name) {
             if ( self.uBO_bcSecret ) { return; }
+            try {
                 const bcSecret = new self.BroadcastChannel(name);
                 bcSecret.onmessage = ev => {
                     const msg = ev.data;
@@ -195,6 +196,8 @@ const onScriptletMessageInjector = (( ) => {
                 };
                 bcSecret.postMessage('iamready!');
                 self.uBO_bcSecret = bcSecret;
+            } catch(_) {
+            }
         }.toString(),
         ')(',
             'bcSecret-slot',