diff --git a/devtools/client/framework/toolbox.js b/devtools/client/framework/toolbox.js
index 6efbacfeb6e3..7fe219155704 100644
--- a/devtools/client/framework/toolbox.js
+++ b/devtools/client/framework/toolbox.js
@@ -1767,16 +1767,12 @@ Toolbox.prototype = {
 
     if (openedConsolePanel) {
       deck.collapsed = true;
-      deck.removeAttribute("expanded");
       splitter.hidden = true;
       webconsolePanel.collapsed = false;
-      webconsolePanel.setAttribute("expanded", "");
     } else {
       deck.collapsed = false;
-      deck.toggleAttribute("expanded", !this.splitConsole);
       splitter.hidden = !this.splitConsole;
       webconsolePanel.collapsed = !this.splitConsole;
-      webconsolePanel.removeAttribute("expanded");
     }
   },
 
diff --git a/devtools/client/themes/common.css b/devtools/client/themes/common.css
index 552d1baf578c..72da70accc5f 100644
--- a/devtools/client/themes/common.css
+++ b/devtools/client/themes/common.css
@@ -12,7 +12,6 @@
    * we're using the `font` shorthand. */
   font: message-box;
   font-size: var(--theme-body-font-size);
-  -moz-box-layout: flex;
 
   --tab-line-hover-color: rgba(0,0,0,.2);
   --tab-line-selected-color: var(--blue-50);
diff --git a/devtools/client/themes/storage.css b/devtools/client/themes/storage.css
index 277dc51c5e8e..9a6c5cbaa080 100644
--- a/devtools/client/themes/storage.css
+++ b/devtools/client/themes/storage.css
@@ -17,9 +17,14 @@ a {
   min-width: 220px;
   max-width: 500px;
   overflow: auto;
-  contain: size;
+}
+
+#storage-tree {
   background: var(--theme-sidebar-background);
-  /* Let the component gain focus when a click hits an empty area */
+}
+
+/* Let the component gain focus when a click hits an empty area */
+#storage-tree {
   -moz-user-focus: normal;
 }
 
@@ -81,7 +86,7 @@ a {
 
 /* Prevent all columns except for value from resizing with the panel */
 #storage-table .table-widget-column:not(#value) {
-  -moz-box-flex: 0;
+  width: 0;
 }
 
 /* Text input in storage table */
diff --git a/devtools/client/themes/toolbox.css b/devtools/client/themes/toolbox.css
index a3ed691e2bdc..ef8866bfc14c 100644
--- a/devtools/client/themes/toolbox.css
+++ b/devtools/client/themes/toolbox.css
@@ -577,20 +577,8 @@
   -moz-box-flex: 1;
 }
 
-#toolbox-panel-webconsole[collapsed],
-#toolbox-deck[collapsed] {
-  height: 0 !important;
-  min-height: 0 !important;
-}
-
-#toolbox-deck:not([collapsed]),
-#toolbox-panel-webconsole[expanded] {
-  /* Override the splitter-set height and flex instead */
-  height: auto !important;
-}
-
 /**
- * Ensure that selected toolbox panel's contents are keyboard accessible as they
+ * Enrure that selected toolbox panel's contents are keyboard accessible as they
  * are explicitly made not to be when hidden (default).
  */
 .toolbox-panel[selected] * {
diff --git a/devtools/client/themes/widgets.css b/devtools/client/themes/widgets.css
index d0f6e9ed8b81..e318a38ec45f 100644
--- a/devtools/client/themes/widgets.css
+++ b/devtools/client/themes/widgets.css
@@ -389,7 +389,6 @@
   width: 100%;
   height: 100%;
   overflow: auto;
-  contain: size;
 }
 
 .table-widget-body[empty="empty"] {
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_split.js b/devtools/client/webconsole/test/browser/browser_webconsole_split.js
index d9cc00ce7561..200fb95a8c20 100644
--- a/devtools/client/webconsole/test/browser/browser_webconsole_split.js
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_split.js
@@ -307,7 +307,7 @@ add_task(async function() {
           currentUIState.webconsoleHeight +
           currentUIState.splitterHeight
       ),
-      Math.round(currentUIState.containerHeight),
+      currentUIState.containerHeight,
       "Everything adds up to container height"
     );
     ok(
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_split_persist.js b/devtools/client/webconsole/test/browser/browser_webconsole_split_persist.js
index 00d624e4affd..983044bcc676 100644
--- a/devtools/client/webconsole/test/browser/browser_webconsole_split_persist.js
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_split_persist.js
@@ -68,6 +68,12 @@ add_task(async function() {
     "The actual height of the console is bound with a min height"
   );
 
+  toolbox.webconsolePanel.style.height = "10000px";
+  ok(
+    toolbox.webconsolePanel.clientHeight < 10000,
+    "The actual height of the console is bound with a max height"
+  );
+
   await toggleSplitConsoleWithEscape(toolbox);
   ok(!toolbox.splitConsole, "Split console is now hidden.");
   is(
@@ -81,7 +87,7 @@ add_task(async function() {
 
   is(
     getHeightPrefValue(),
-    1,
+    10000,
     "Height is set based on panel height after closing"
   );
 
diff --git a/toolkit/themes/shared/global-shared.css b/toolkit/themes/shared/global-shared.css
index 477a6e91f471..af4cf4b6133a 100644
--- a/toolkit/themes/shared/global-shared.css
+++ b/toolkit/themes/shared/global-shared.css
@@ -107,7 +107,6 @@ xul|iframe {
   border: none;
   min-width: 10px;
   min-height: 10px;
-  contain: size;
 }
 
 /* Label/description formatting */