diff --git a/packages/starlight/components/Select.astro b/packages/starlight/components/Select.astro
index 369bc3c3eda..a6ebc1b3fc0 100644
--- a/packages/starlight/components/Select.astro
+++ b/packages/starlight/components/Select.astro
@@ -78,6 +78,28 @@ interface Props {
 			color: var(--sl-color-gray-1);
 		}
 
+		/*
+		 * Firefox on Windows renders native select option dropdowns with
+		 * incorrect colors in dark mode — option backgrounds appear white
+		 * and checked/hovered text is invisible. Use @supports to target
+		 * Firefox (-moz-appearance) so other browsers are unaffected.
+		 * Only fix option backgrounds, not the select itself, to preserve
+		 * transparent backgrounds on pages like the homepage.
+		 * See: https://github.com/withastro/starlight/issues/3426
+		 */
+		@supports (-moz-appearance: none) {
+			:global([data-theme='dark']) select option,
+			:global([data-theme='dark']) select option:checked {
+				background-color: var(--sl-color-bg-nav);
+				color: var(--sl-color-text);
+			}
+
+			:global([data-theme='dark']) select option:hover {
+				background-color: var(--sl-color-accent-high);
+				color: var(--sl-color-text-invert);
+			}
+		}
+
 		@media (min-width: 50rem) {
 			select {
 				font-size: var(--sl-text-sm);