Add informative tooltip re. unprocessed requests at launch

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/2585

platform/common/vapi-background.js

@@ -731,9 +731,8 @@ if ( webext.browserAction instanceof Object ) {
 
 {
     const browserAction = vAPI.browserAction;
-    const  titleTemplate =
-        browser.runtime.getManifest().browser_action.default_title +
-        ' ({badge})';
+    const titleTemplate = `${browser.runtime.getManifest().browser_action.default_title} ({badge})`;
+    const browserLaunchIssue = browser.i18n.getMessage('unprocessedRequestTooltip');
     const icons = [
         { path: {
             '16': 'img/icon_16-off.png',
@@ -840,8 +839,9 @@ if ( webext.browserAction instanceof Object ) {
         const tab = await vAPI.tabs.get(tabId);
         if ( tab === null ) { return; }
 
+        const hasUnprocessedRequest = vAPI.net && vAPI.net.hasUnprocessedRequest(tabId);
         const { parts, state } = details;
-        const { badge, color } = vAPI.net && vAPI.net.hasUnprocessedRequest(tabId)
+        const { badge, color } = hasUnprocessedRequest
                 ? { badge: '!', color: '#FC0' }
                 : details;
 
@@ -866,13 +866,11 @@ if ( webext.browserAction instanceof Object ) {
         // - the platform does not support browserAction.setIcon(); OR
         // - the rendering of the badge is disabled
         if ( browserAction.setTitle !== undefined ) {
-            browserAction.setTitle({
-                tabId: tab.id,
-                title: titleTemplate.replace(
-                    '{badge}',
+            const title = hasUnprocessedRequest && browserLaunchIssue ||
+                titleTemplate.replace('{badge}',
                     state === 1 ? (badge !== '' ? badge : '0') : 'off'
-                )
-            });
+                );
+            browserAction.setTitle({ tabId: tab.id, title });
         }
 
         if ( vAPI.contextMenu instanceof Object ) {

src/_locales/en/messages.json

@@ -1269,6 +1269,10 @@
     "message": "Errors: {{count}}",
     "description": "Summary of number of errors as reported by the linter "
   },
+  "unprocessedRequestTooltip": {
+    "message": "Could not filter properly at browser launch.\nReload the page to ensure proper filtering",
+    "description": "Tooltip for the toolbar icon. Use newline character(s) where appropriate to prevent tooltip from being too long horizontally"
+  },
   "dummy": {
     "message": "This entry must be the last one",
     "description": "so we dont need to deal with comma for last entry"