diff --git a/browser/themes/shared/devtools/performance.inc.css b/browser/themes/shared/devtools/performance.inc.css
index 6a06023f9d23..5c55254c110a 100644
--- a/browser/themes/shared/devtools/performance.inc.css
+++ b/browser/themes/shared/devtools/performance.inc.css
@@ -3,20 +3,26 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+/* CSS Variables specific to this panel that aren't defined by the themes */
+.theme-dark {
+  --cell-border-color: rgba(255,255,255,0.15);
+  --focus-cell-border-color: rgba(255,255,255,0.5);
+  --row-alt-background-color: rgba(29,79,115,0.15);
+  --row-hover-background-color: rgba(29,79,115,0.25);
+}
+
+.theme-light {
+  --cell-border-color: rgba(0,0,0,0.15);
+  --focus-cell-border-color: rgba(0,0,0,0.3);
+  --row-alt-background-color: rgba(76,158,217,0.1);
+  --row-hover-background-color: rgba(76,158,217,0.2);
+}
+
 /* Toolbar */
 
+#performance-toolbar > tabs,
 #performance-toolbar {
-  -moz-border-end: 1px solid;
-}
-
-.theme-dark #performance-toolbar > tabs,
-.theme-dark #performance-toolbar {
-  -moz-border-end-color: #000; /* Splitters */
-}
-
-.theme-light #performance-toolbar > tabs,
-.theme-light #performance-toolbar {
-  -moz-border-end-color: #aaa; /* Splitters */
+  -moz-border-end-color: var(--theme-splitter-color);
 }
 
 /* Overview Panel */
@@ -85,23 +91,14 @@
   -moz-box-align: center;
   overflow: hidden;
   padding: 1px 4px;
+  color: var(--theme-body-color);
+  -moz-border-end-color: var(--cell-border-color);
 }
 
 .call-tree-header:not(:last-child),
 .call-tree-cell:not(:last-child) {
-  -moz-border-end: 1px solid;
-}
-
-.theme-dark .call-tree-header,
-.theme-dark .call-tree-cell {
-  -moz-border-end-color: rgba(255,255,255,0.15);
-  color: #8fa1b2; /* Body Text */
-}
-
-.theme-light .call-tree-header,
-.theme-light .call-tree-cell {
-  -moz-border-end-color: rgba(0,0,0,0.15);
-  color: #18191a; /* Body Text */
+  -moz-border-end-width: 1px;
+  -moz-border-end-style: solid;
 }
 
 .call-tree-header:not(:last-child) {
@@ -112,56 +109,32 @@
   text-align: end;
 }
 
-.theme-dark .call-tree-header {
-  background-color: #252c33; /* Tab Toolbar */
+.call-tree-header {
+  background-color: var(--theme-tab-toolbar-background);
 }
 
-.theme-light .call-tree-header {
-  background-color: #ebeced; /* Tab Toolbar */
+.call-tree-item:last-child:not(:focus) {
+  border-bottom: 1px solid var(--cell-border-color);
 }
 
-.theme-dark .call-tree-item:last-child:not(:focus) {
-  border-bottom: 1px solid rgba(255,255,255,0.15);
+.call-tree-item:nth-child(2n) {
+  background-color: var(--row-alt-background-color);
 }
 
-.theme-light .call-tree-item:last-child:not(:focus) {
-  border-bottom: 1px solid rgba(0,0,0,0.15);
+.call-tree-item:hover {
+  background-color: var(--row-hover-background-color);
 }
 
-.theme-dark .call-tree-item:nth-child(2n) {
-  background-color: rgba(29,79,115,0.15);
-}
-
-.theme-light .call-tree-item:nth-child(2n) {
-  background-color: rgba(76,158,217,0.1);
-}
-
-.theme-dark .call-tree-item:hover {
-  background-color: rgba(29,79,115,0.25);
-}
-
-.theme-light .call-tree-item:hover {
-  background-color: rgba(76,158,217,0.2);
-}
-
-.theme-dark .call-tree-item:focus {
-  background-color: #1d4f73; /* Select Highlight Blue */
-}
-
-.theme-light .call-tree-item:focus {
-  background-color: #4c9ed9; /* Select Highlight Blue */
+.call-tree-item:focus {
+  background-color: var(--theme-selection-background);
 }
 
 .call-tree-item:focus label {
-  color: #f5f7fa !important; /* Light foreground text */
+  color: var(--theme-selection-color) !important;
 }
 
-.theme-dark .call-tree-item:focus .call-tree-cell {
-  -moz-border-end-color: rgba(0,0,0,0.3);
-}
-
-.theme-light .call-tree-item:focus .call-tree-cell {
-  -moz-border-end-color: rgba(255,255,255,0.5);
+.call-tree-item:focus .call-tree-cell {
+  -moz-border-end-color: var(--focus-cell-border-color);
 }
 
 .call-tree-item:not([origin="content"]) .call-tree-name,
@@ -180,33 +153,18 @@
   text-decoration: underline;
 }
 
-.theme-dark .call-tree-url {
-  color: #46afe3;
+.call-tree-url {
+  color: var(--theme-highlight-blue);
 }
 
-.theme-light .call-tree-url {
-  color: #0088cc;
-}
-
-.theme-dark .call-tree-line {
-  color: #d96629;
-}
-
-.theme-light .call-tree-line {
-  color: #f13c00;
+.call-tree-line {
+  color: var(--theme-highlight-orange);
 }
 
 .call-tree-host {
   -moz-margin-start: 8px !important;
   font-size: 90%;
-}
-
-.theme-dark .call-tree-host {
-  color: #8fa1b2;
-}
-
-.theme-light .call-tree-host {
-  color: #8fa1b2;
+  color: var(--theme-content-color2);
 }
 
 .call-tree-url[value=""],
@@ -307,15 +265,7 @@
 }
 
 .waterfall-sidebar {
-  -moz-border-end: 1px solid;
-}
-
-.theme-dark .waterfall-sidebar {
-  -moz-border-end-color: #000;
-}
-
-.theme-light .waterfall-sidebar {
-  -moz-border-end-color: #aaa;
+  -moz-border-end: 1px solid var(--theme-splitter-color);
 }
 
 .waterfall-marker-container:hover > .waterfall-sidebar {
@@ -330,14 +280,7 @@
   width: 100px;
   font-size: 9px;
   transform-origin: left center;
-}
-
-.theme-dark .waterfall-header-tick {
-  color: #a9bacb;
-}
-
-.theme-light .waterfall-header-tick {
-  color: #292e33;
+  color: var(--theme-body-color);
 }
 
 .waterfall-header-tick:not(:first-child) {
@@ -365,21 +308,14 @@
   transform-origin: left center;
 }
 
-.theme-light .waterfall-marker-container.selected > .waterfall-sidebar,
-.theme-light .waterfall-marker-container.selected > .waterfall-marker-item {
-  background-color: #4c9ed9; /* Select Highlight Blue */
-  color: #f5f7fa; /* Light foreground text */
-}
-
-.theme-dark .waterfall-marker-container.selected > .waterfall-sidebar,
-.theme-dark .waterfall-marker-container.selected > .waterfall-marker-item {
-  background-color: #1d4f73; /* Select Highlight Blue */
-  color: #f5f7fa; /* Light foreground text */
+.waterfall-marker-container.selected > .waterfall-marker-item {
+  background-color: var(--theme-selection-background);
+  color: var(--theme-selection-color);
 }
 
 .waterfall-marker-container.selected .waterfall-marker-bullet,
 .waterfall-marker-container.selected .waterfall-marker-bar {
-  border-color: initial!important;
+  border-color: initial !important;
 }
 
 #waterfall-details {