--- a/browser/base/content/test/static/browser_parsable_css.js
+++ b/browser/base/content/test/static/browser_parsable_css.js
@@ -112,19 +112,16 @@ let whitelist = [
   {propName: "--theme-codemirror-gutter-background",
    isFromDevTools: true},
   // Bug 1441879
   {propName: "--arrow-width",
    isFromDevTools: true},
   // Bug 1442300
   {propName: "--in-content-category-background",
    isFromDevTools: false},
-  // Bug 1442314
-  {propName: "--separator-border-image",
-   isFromDevTools: true},
 
   // Used on Linux
   {propName: "--in-content-box-background-odd",
    platforms: ["win", "macosx"],
    isFromDevTools: false},
 
   // These properties *are* actually referenced. Need to find why
   // their reference isn't getting counted.

--- a/devtools/client/themes/toolbars.css
+++ b/devtools/client/themes/toolbars.css
@@ -76,18 +76,17 @@
 
 .devtools-toolbar-bottom {
   border-top-width: 1px;
   border-bottom: none;
 }
 
 .devtools-separator {
   border-inline-start: 1px solid;
-  border-image: var(--separator-border-image);
-  border-image-slice: 1;
+  border-image: var(--separator-border-image) 1 1;
   height: inherit;
 }
 
 /* In-tools sidebar */
 .devtools-sidebar-tabs {
   -moz-appearance: none;
   margin: 0;
   height: 100%;