Bug 1453803 - Increase the opacity of the default border color for WebExtension popups. r=ntim

MozReview-Commit-ID: AeDmPJtPdBE

--HG--
extra : rebase_source : 56a6e4231e55770cd8d488941b2fd0ce1f69fe89

browser/components/extensions/ExtensionPopups.jsm

@@ -368,7 +368,7 @@ class BasePopup {
     this.panel.style.setProperty("--arrowpanel-background", background);
     if (background == "#fff") {
       // Set a usable default color that work with the default background-color.
-      this.panel.style.setProperty("--arrowpanel-border-color", "hsla(210,4%,10%,.05)");
+      this.panel.style.setProperty("--arrowpanel-border-color", "hsla(210,4%,10%,.15)");
     }
     this.background = background;
   }