diff --git a/chrome/content/scaffold/load.xhtml b/chrome/content/scaffold/load.xhtml
index 67e295dad8..dc4a18e507 100644
--- a/chrome/content/scaffold/load.xhtml
+++ b/chrome/content/scaffold/load.xhtml
@@ -24,7 +24,6 @@
     ***** END LICENSE BLOCK *****
 -->
 <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
-<?xml-stylesheet href="chrome://zotero/skin/scaffold.css" type="text/css"?>
 <?xml-stylesheet href="chrome://zotero/skin/zotero.css" type="text/css"?>
 <?xml-stylesheet href="chrome://zotero-platform/content/zotero.css"?>
 
@@ -40,6 +39,6 @@
 	id="scaffold-load">
 	<script src="load.js"/>
 	<script src="chrome://zotero/content/titlebar.js"/>
-	<richlistbox id="listbox" class="theme-listbox"/>
+	<richlistbox id="listbox" class="theme-listbox" style="height: 300px;"/>
 </dialog>
 </window>
diff --git a/chrome/content/scaffold/scaffold.xhtml b/chrome/content/scaffold/scaffold.xhtml
index e3aa941c00..239ca457a8 100644
--- a/chrome/content/scaffold/scaffold.xhtml
+++ b/chrome/content/scaffold/scaffold.xhtml
@@ -467,7 +467,7 @@
 						</vbox>
 					</tabpanel>
 					<tabpanel flex="1" id="tabpanel-tests">
-						<vbox flex="1" style="max-width: 100%;">
+						<vbox id="testing-container">
 							<vbox id="testing-listbox-container">
 								<keyset>
 									<key id="key-delete-tests" observes="validate-tests" keycode="VK_BACK" oncommand="Scaffold.deleteSelectedTests()"/>
@@ -487,27 +487,27 @@
 									onselect="Scaffold.handleTestSelect(event)"
 									context="testing-context-menu"
 								/>
-								<hbox>
-									<button observes="validate-tests" label="&scaffold.testing.delete;" tooltiptext="Delete the selected tests" oncommand="Scaffold.deleteSelectedTests()"/>
-									<button observes="validate-tests" label="&scaffold.testing.run;" tooltiptext="Run the selected tests" oncommand="Scaffold.runSelectedTests()"/>
-									<button observes="validate-tests" label="&scaffold.testing.update;" tooltiptext="Run the selected tests and update the test definitions with the latest data" oncommand="Scaffold.updateSelectedTests()"/>
-
-									<hbox flex="1" pack="end">
-										<checkbox
-											id="checkbox-remember-cookies"
-											label="&scaffold.testing.rememberCookies;"
-											native="true"
-											checked="true"
-										/>
-									</hbox>
-								</hbox>
 							</vbox>
+							<hbox id="testing-buttons">
+								<button observes="validate-tests" label="&scaffold.testing.delete;" tooltiptext="Delete the selected tests" oncommand="Scaffold.deleteSelectedTests()"/>
+								<button observes="validate-tests" label="&scaffold.testing.run;" tooltiptext="Run the selected tests" oncommand="Scaffold.runSelectedTests()"/>
+								<button observes="validate-tests" label="&scaffold.testing.update;" tooltiptext="Run the selected tests and update the test definitions with the latest data" oncommand="Scaffold.updateSelectedTests()"/>
+
+								<hbox flex="1" pack="end">
+									<checkbox
+										id="checkbox-remember-cookies"
+										label="&scaffold.testing.rememberCookies;"
+										native="true"
+										checked="true"
+									/>
+								</hbox>
+							</hbox>
 							<iframe src="monaco/monaco.html" id="editor-tests" onmousedown="this.focus()"/>
 						</vbox>
 					</tabpanel>
 					<tabpanel>
-						<vbox flex="1">
-							<hbox align="center">
+						<vbox id="browser-container">
+							<hbox id="browser-url-container" align="center">
 								<label control="browser-url" value="&scaffold.tabUrl.label;"/>
 								<html:input id="browser-url" style="flex: 1;"/>
 								<button observes="validate-tests" label="&scaffold.testing.create.web;" tooltiptext="Create a new test from the current page" oncommand="Scaffold.saveTestFromCurrent('web')"/>
@@ -524,8 +524,8 @@
 						</vbox>
 					</tabpanel>
 					<tabpanel flex="1" id="tabpanel-import">
-						<vbox flex="1">
-							<hbox align="right">
+						<vbox id="import-container">
+							<hbox id="import-buttons" align="right">
 								<button observes="validate-tests" label="&scaffold.testing.create.import;" tooltiptext="Create a new test from the current import data" oncommand="Scaffold.saveTestFromCurrent('import')" />
 								<button observes="validate-tests" label="&scaffold.testing.create.search;" tooltiptext="Create a new test from the current search data" oncommand="Scaffold.saveTestFromCurrent('search')" />
 							</hbox>
diff --git a/scss/components/_listheader.scss b/scss/components/_listheader.scss
index 7879e464f5..dd6dcdbd67 100644
--- a/scss/components/_listheader.scss
+++ b/scss/components/_listheader.scss
@@ -10,24 +10,43 @@ richlistbox {
 	border: var(--material-panedivider);
 }
 
-treecol {
-	appearance: none;
-	border: none;
+listheader {
+	treecol {
+		appearance: none;
+		border: none;
+		background: transparent;
+		padding: 0;
+		
+		.treecol-text {
+			padding: 0 4px;
+			margin: 1px 6px 2px 5px !important;
+		}
 
-    background: transparent;
+		&::after {
+			content: "";
+			display: block;
+			height: 100%;
+			width: 1px;
+			background: linear-gradient(var(--fill-quarternary), var(--fill-quarternary)) no-repeat center/1px 66.666667%;
+		}
 
-    &:hover {
-        background: var(--material-mix-quinary);
-    }
-
-    &:hover:active {
-        background: var(--material-mix-quarternary);
-    }
+		&:last-of-type::after {
+			display: none;
+		}
+	
+		&:hover {
+			background: var(--material-mix-quinary);
+		}
+	
+		&:hover:active {
+			background: var(--material-mix-quarternary);
+		}
+	}
 }
 
 listheader + richlistbox {
 	margin-top: 0;
-	border-top: none;
+	border-top: none !important;
 }
 
 select[size][multiple] > option,
diff --git a/scss/components/_richlistbox.scss b/scss/components/_richlistbox.scss
index 0865dc9d0a..5e542acd5a 100644
--- a/scss/components/_richlistbox.scss
+++ b/scss/components/_richlistbox.scss
@@ -1,6 +1,8 @@
 richlistbox.theme-listbox {
 	background: var(--material-background);
 	border: var(--material-panedivider);
+	// Prevent horizontal scrollbar on Windows
+	overflow-x: hidden;
 
 	richlistitem {
 		--listitem-selectedBackground: var(--tag-gray);
@@ -23,11 +25,12 @@ richlistitem {
 	padding: 0.2em 0.4em;
 }
 
-richlistitem, richlistitem > * {
+richlistitem, richlistitem * {
 	// Prevent word cut-off with double-byte characters
 	overflow: hidden;
 	white-space: nowrap;
 	text-overflow: ellipsis;
+	width: 100%;
 }
 
 richlistcheckbox[selected=true] {
diff --git a/scss/mac/_tabbox.scss b/scss/mac/_tabbox.scss
index a43cf1b715..33372ef996 100644
--- a/scss/mac/_tabbox.scss
+++ b/scss/mac/_tabbox.scss
@@ -4,45 +4,60 @@ tabbox {
 			appearance: none;
 			// Since the tab with opacity is weird, we just use hard-coded colors
 			@include light-dark(background, #ededed, #343434);
-			box-shadow:
+			--tabbox-tab-shadow:
 				0px 2px 2px -2px var(--fill-quarternary) inset,
 				0px -2px 2px -2px var(--fill-quarternary) inset,
 				0px 4px 4px -4px var(--fill-quinary) inset,
 				0px -4px 4px -4px var(--fill-quinary) inset;
+			--tabbox-tab-shadow-left:
+				2px 0px 2px -2px var(--fill-quarternary) inset,
+				4px 0px 4px -4px var(--fill-quinary) inset;
+			--tabbox-tab-shadow-right:
+				-2px 0px 2px -2px var(--fill-quarternary) inset,
+				-4px 0px 4px -4px var(--fill-quinary) inset;
+			
+			box-shadow: var(--tabbox-tab-shadow);
 
 			&::before {
 				content: "";
-				position: absolute;
 				height: 14px;
 				top: 5px;
 				border-left: 1px solid var(--fill-quarternary);
 			}
 
 			&:first-of-type {
-				border-top-left-radius: 5px;
-				border-bottom-left-radius: 5px;
-				box-shadow:
-					0px 2px 2px -2px var(--fill-quarternary) inset,
-					0px -2px 2px -2px var(--fill-quarternary) inset,
-					0px 4px 4px -4px var(--fill-quinary) inset,
-					0px -4px 4px -4px var(--fill-quinary) inset,
-					2px 0px 2px -2px var(--fill-quarternary) inset,
-					4px 0px 4px -4px var(--fill-quinary) inset;
+				border-start-start-radius: 6px;
+				border-end-start-radius: 6px;
+				
 				&::before {
 					display: none;
 				}
+
+				&:-moz-locale-dir(ltr) {
+					box-shadow:
+						var(--tabbox-tab-shadow),
+						var(--tabbox-tab-shadow-left);
+				}
+				&:-moz-locale-dir(rtl) {
+					box-shadow:
+						var(--tabbox-tab-shadow),
+						var(--tabbox-tab-shadow-right);
+				}
 			}
 
 			&:last-of-type {
-				border-top-right-radius: 5px;
-				border-bottom-right-radius: 5px;
-				box-shadow:
-					0px 2px 2px -2px var(--fill-quarternary) inset,
-					0px -2px 2px -2px var(--fill-quarternary) inset,
-					0px 4px 4px -4px var(--fill-quinary) inset,
-					0px -4px 4px -4px var(--fill-quinary) inset,
-					-2px 0px 2px -2px var(--fill-quarternary) inset,
-					-4px 0px 4px -4px var(--fill-quinary) inset;
+				border-start-end-radius: 6px;
+				border-end-end-radius: 6px;
+				&:-moz-locale-dir(ltr) {
+					box-shadow:
+						var(--tabbox-tab-shadow),
+						var(--tabbox-tab-shadow-right);
+				}
+				&:-moz-locale-dir(rtl) {
+					box-shadow:
+						var(--tabbox-tab-shadow),
+						var(--tabbox-tab-shadow-left);
+				}
 			}
 
 			&[visuallyselected=true] {
@@ -53,12 +68,12 @@ tabbox {
 
 				& + tab {
 					&::before {
-						display: none;
+						border-color: transparent;
 					}
 				}
 
 				&::before {
-					display: none;
+					border-color: transparent;
 				}
 
 				.tab-middle {
@@ -68,6 +83,8 @@ tabbox {
 						0px 1px 0.75px 0px var(--fill-quinary),
 						0px 0.25px 0.25px 0px var(--color-border);;
 					border: 0.5px solid var(--fill-senary);
+					padding: 0.5px 6px 0.5px;
+					margin: 0px -0.5px 1px -0.5px;
 				}
 			}
 		}
diff --git a/scss/scaffold.scss b/scss/scaffold.scss
index 9fd6beeb9b..c380fd8a05 100644
--- a/scss/scaffold.scss
+++ b/scss/scaffold.scss
@@ -52,7 +52,6 @@ $scaffold-toolbarbutton-icons: (
 	border-bottom: var(--material-panedivider);
 
 	toolbarbutton {
-		width: 28px;
 		height: 28px;
 		padding: 0 4px;
 		margin: 0 4px;
@@ -65,57 +64,11 @@ $scaffold-toolbarbutton-icons: (
 	toolbarseparator {
 		appearance: none;
 		width: 1px;
-		height: 20px;
+		height: 18px;
 		background-color: var(--fill-quinary);
 	}
 }
 
-#metadata-grid {
-	flex: 1;
-	display: grid;
-	align-content: start;
-	align-items: center;
-	grid-template-columns: max-content 1fr;
-}
-
-#metadata-grid > label:nth-child(2n + 1) {
-	justify-self: right;
-}
-
-.button-row {
-	display: grid;
-	grid-template-columns: 1fr max-content;
-}
-
-#metadata-bottom-row {
-	display: flex;
-	align-items: center;
-}
-
-#metadata-bottom-row #textbox-minVersion {
-	margin-right: auto;
-}
-
-#hbox-testFrame {
-	-moz-box-align: center;
-}
-
-richlistbox {
-	min-width: 200px;
-
-	richlistitem {
-		align-items: center;
-
-		> hbox {
-			display: block;
-		}
-	}
-}
-
-#zotero-toolbar toolbarseparator {
-	height: 18px;
-}
-
 browser,
 #appcontent
 {
@@ -126,10 +79,6 @@ browser,
 	padding: 16px;
 }
 
-vbox > splitter {
-	cursor: row-resize;
-}
-
 #left-tabbox {
 	flex: 1;
 	min-width: 500px;
@@ -143,20 +92,11 @@ vbox > splitter {
 	}
 }
 
-#checkboxes-translatorType {
-	display: flex;
-	flex-direction: row;
-	gap: 10px;
-}
-
-#tabpanel-metadata label:first-child {
-	text-align: right;
-}
-
 #right-pane {
 	min-width: 350px;
-	margin: -16px -16px -16px 0px;
-	border-left: var(--material-panedivider);
+	margin: -16px;
+	margin-inline-start: 0;
+	border-inline-start: var(--material-panedivider);
 
 	#output {
 		width: 100%;
@@ -167,17 +107,111 @@ vbox > splitter {
 	}
 }
 
-#scaffold-load {
-	#listbox {
-		height: 300px;
+#metadata-grid {
+	flex: 1;
+	display: grid;
+	align-content: start;
+	align-items: center;
+	grid-template-columns: max-content 1fr;
+	gap: 8px;
+
+	label,
+	button,
+	input {
+		margin: 0;
+	}
+
+	& > label:nth-child(2n + 1) {
+		justify-self: inline-end;
+	}
+
+	label:first-child {
+		text-align: inline-end;
+	}
+
+	.button-row {
+		display: grid;
+		grid-template-columns: 1fr max-content;
+		gap: 8px;
+	}
+
+	#metadata-bottom-row {
+		display: flex;
+		align-items: center;
+		gap: 8px;
+	
+		#textbox-minVersion {
+			margin-inline-end: auto;
+		}
+	}
+
+	#checkboxes-translatorType {
+		display: flex;
+		flex-direction: row;
+		gap: 8px;
 	}
 }
 
-#testing-listbox-container {
+#testing-container {
 	flex: 1;
+	max-width: 100%;
+	gap: 8px;
+
+	richlistbox {
+		min-width: 200px;
+		margin-block: 0;
+	
+		richlistitem {
+			align-items: center;
+	
+			> hbox {
+				display: block;
+			}
+		}
+	}
+
+	#testing-buttons {
+		gap: 8px;
+
+		button,
+		checkbox {
+			margin: 0;
+		}
+	}
+
+	#testing-listbox-container {
+		flex: 1;
+	}
+
+	#editor-tests {
+		flex: 2;
+	}
 }
 
-#editor-tests {
-	flex: 2;
-	margin-top: 3px;
+#browser-container {
+	flex: 1;
+	gap: 8px;
+
+	#browser-url-container {
+		gap: 8px;
+
+		button,
+		label,
+		input {
+			margin: 0;
+		}
+	}	
+}
+
+#import-container {
+	flex: 1;
+	gap: 8px;
+
+	#import-buttons {
+		gap: 8px;
+
+		button {
+			margin: 0;
+		}
+	}
 }
diff --git a/scss/win/components/_tabbox.scss b/scss/win/components/_tabbox.scss
index ae62625277..d8bb2bb2e2 100644
--- a/scss/win/components/_tabbox.scss
+++ b/scss/win/components/_tabbox.scss
@@ -24,15 +24,15 @@ tabbox {
 			color-scheme: light dark;
 
 			&:first-of-type {
-				border-top-left-radius: 4px;
-				border-bottom-left-radius: 4px;
-				border-left: 1px solid var(--fill-quinary);
+				border-start-start-radius: 4px;
+				border-end-start-radius: 4px;
+				border-inline-start: 1px solid var(--fill-quinary);
 			}
 
 			&:last-of-type {
-				border-top-right-radius: 4px;
-				border-bottom-right-radius: 4px;
-				border-right: 1px solid var(--fill-quinary);
+				border-start-end-radius: 4px;
+				border-end-end-radius: 4px;
+				border-inline-end: 1px solid var(--fill-quinary);
 			}
 
 			@include focus-ring;