Inject scriptlets at webNavigation.onCommitted time in Firefox

Just as is the case with Chromium.

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/1694

src/js/background.js

@@ -127,7 +127,6 @@ const µBlock = {  // jshint ignore:line
     privacySettingsSupported: vAPI.browserSettings instanceof Object,
     cloudStorageSupported: vAPI.cloud instanceof Object,
     canFilterResponseData: typeof browser.webRequest.filterResponseData === 'function',
-    canInjectScriptletsNow: vAPI.webextFlavor.soup.has('chromium'),
 
     // https://github.com/chrisaljoudi/uBlock/issues/180
     // Whitelist directives need to be loaded once the PSL is available

src/js/messaging.js

@@ -627,10 +627,7 @@ const retrieveContentScriptParameters = async function(sender, request) {
     // https://github.com/uBlockOrigin/uBlock-issues/issues/688#issuecomment-748179731
     //   For non-network URIs, scriptlet injection is deferred to here. The
     //   effective URL is available here in `request.url`.
-    if (
-        µb.canInjectScriptletsNow === false ||
-        isNetworkURI(sender.frameURL) === false
-    ) {
+    if ( isNetworkURI(sender.frameURL) === false ) {
         response.scriptlets = scriptletFilteringEngine.retrieve(request);
     }
 

src/js/tab.js

@@ -913,11 +913,7 @@ vAPI.Tabs = class extends vAPI.Tabs {
         const pageStore = µb.pageStoreFromTabId(tabId);
         if ( pageStore === null ) { return; }
         pageStore.setFrameURL(details);
-        if (
-            µb.canInjectScriptletsNow &&
-            isNetworkURI(url) &&
-            pageStore.getNetFilteringSwitch()
-        ) {
+        if ( isNetworkURI(url) && pageStore.getNetFilteringSwitch() ) {
             scriptletFilteringEngine.injectNow(details);
         }
     }