--- a/toolkit/themes/shared/media/videocontrols.css
+++ b/toolkit/themes/shared/media/videocontrols.css
@@ -198,17 +198,17 @@ audio > xul|videocontrols {
   display: flex;
   flex-direction: column;
   justify-content: center;
   align-items: center;
 }
 
 .progressStack {
   position: relative;
-  width: 100%;
+  width: calc(100% - 2.5px);
   height: 5px;
 }
 
 .scrubberStack {
   min-width: 48px;
   flex-basis: 48px;
   flex-grow: 2;
   flex-shrink: 0;