diff --git a/chrome/content/scaffold/scaffold.xhtml b/chrome/content/scaffold/scaffold.xhtml
index b426643c76..36b52a61ec 100644
--- a/chrome/content/scaffold/scaffold.xhtml
+++ b/chrome/content/scaffold/scaffold.xhtml
@@ -502,7 +502,6 @@
 									</hbox>
 								</hbox>
 							</vbox>
-							<splitter/>
 							<iframe src="monaco/monaco.html" id="editor-tests" onmousedown="this.focus()"/>
 						</vbox>
 					</tabpanel>
diff --git a/scss/abstracts/_mixins.scss b/scss/abstracts/_mixins.scss
index 346ddcc1d2..351530b819 100644
--- a/scss/abstracts/_mixins.scss
+++ b/scss/abstracts/_mixins.scss
@@ -307,4 +307,13 @@
 	--material-panedivider: 1px solid var(--color-panedivider);
 	--material-border-quinary: 1px solid var(--fill-quinary);
 	--material-border-quarternary: 1px solid var(--fill-quarternary);
-}
\ No newline at end of file
+}
+
+@mixin contain-richlistbox {
+	// richlistbox elements are crazy and will expand beyond the window size
+	// unless all/most elements in the hierarchy that contain that
+	// richlistbox have a min-height: 0 set
+	vbox, hbox {
+		min-height: 0;
+	}
+}
diff --git a/scss/components/_selectItemsDialog.scss b/scss/components/_selectItemsDialog.scss
index b950784761..198744a486 100644
--- a/scss/components/_selectItemsDialog.scss
+++ b/scss/components/_selectItemsDialog.scss
@@ -42,7 +42,5 @@
 // unless all/most elements in the hierarchy that contain that
 // richlistbox have a min-height: 0 set
 .contain-richlistbox {
-    vbox, hbox {
-        min-height: 0;
-    }
-}
\ No newline at end of file
+    @include contain-richlistbox;
+}
diff --git a/scss/scaffold.scss b/scss/scaffold.scss
index 472aea50e2..9fd6beeb9b 100644
--- a/scss/scaffold.scss
+++ b/scss/scaffold.scss
@@ -31,6 +31,7 @@ $scaffold-toolbarbutton-icons: (
 
 #scaffold {
 	min-height: 600px;
+	@include contain-richlistbox;
 }
 
 .menubar-container {
@@ -178,4 +179,5 @@ vbox > splitter {
 
 #editor-tests {
 	flex: 2;
+	margin-top: 3px;
 }