Bug 1697943 - Apply a uniform weight to PopupNotification descriptions. r=prathiksha

Differential Revision: https://phabricator.services.mozilla.com/D109550

browser/themes/shared/browser.inc.css

@@ -936,6 +936,13 @@ popupnotificationcontent {
   opacity: 0.7;
 }
 
+.popup-notification-description > b {
+  font-weight: inherit;
+}
+
+.popup-notification-description {
+  font-weight: 600;
+}
 } /** END Proton **/
 
 #tab-notification-deck {