Adds new text for Firefox screen-sharing permission denied error.

conference.js

         let titleKey;
 
         if (error.name === JitsiTrackErrors.PERMISSION_DENIED) {
-            descriptionKey = 'dialog.screenSharingPermissionDeniedError';
-            titleKey = 'dialog.screenSharingFailedToInstallTitle';
+
+            // in FF the only option for user is to deny access temporary or
+            // permanently and we only receive permission_denied
+            // we always show some info cause in case of permanently, no info
+            // shown will be bad experience
+            //
+            // TODO: detect interval between requesting permissions and received
+            // error, this way we can detect user interaction which will have
+            // longer delay
+            if (JitsiMeetJS.util.browser.isFirefox()) {
+                descriptionKey
+                    = 'dialog.screenSharingFirefoxPermissionDeniedError';
+                titleKey = 'dialog.screenSharingFirefoxPermissionDeniedTitle';
+            } else {
+                descriptionKey = 'dialog.screenSharingPermissionDeniedError';
+                titleKey = 'dialog.screenSharingFailedToInstallTitle';
+            }
         } else {
             descriptionKey = 'dialog.screenSharingFailedToInstall';
             titleKey = 'dialog.screenSharingFailedToInstallTitle';

lang/main.json

         "permissionDenied": "Permission Denied",
         "screenSharingFailedToInstall": "Oops! Your screen sharing extension failed to install.",
         "screenSharingFailedToInstallTitle": "Screen sharing extension failed to install",
+        "screenSharingFirefoxPermissionDeniedError": "Something went wrong while we were trying to share your screen. Please make sure that you have given us permission to do so. ",
+        "screenSharingFirefoxPermissionDeniedTitle": "Oops! We weren’t able to start screen sharing!",
         "screenSharingPermissionDeniedError": "Oops! Something went wrong with your screen sharing extension permissions. Please reload and try again.",
         "cameraUnsupportedResolutionError": "Your camera does not support required video resolution.",
         "cameraUnknownError": "Cannot use camera for an unknown reason.",