diff --git a/docs/api-contract.md b/docs/api-contract.md
index 0353b649..84023811 100644
--- a/docs/api-contract.md
+++ b/docs/api-contract.md
@@ -936,6 +936,7 @@ _No props beyond HTML attributes and `UIBaseProps`._
 
 ```ts
 extensionUrl?: string
+icon?: string | JSX.Element
 onDismiss?: () => void
 onInstall?: () => void
 storageKey?: string
diff --git a/src/components/immersive-landing/components/FirefoxPWABanner.tsx b/src/components/immersive-landing/components/FirefoxPWABanner.tsx
index a3dde2da..d72b6ad4 100644
--- a/src/components/immersive-landing/components/FirefoxPWABanner.tsx
+++ b/src/components/immersive-landing/components/FirefoxPWABanner.tsx
@@ -135,7 +135,7 @@ export const FirefoxPWABanner: Component<FirefoxPWABannerProps> = (props) => {
             aria-label={texts().closeLabel}
           >
             <Icon
-              src="icon-[mdi--close]"
+              src="icon-[lucide--x]"
               width={16}
               height={16}
             />
@@ -148,13 +148,15 @@ export const FirefoxPWABanner: Component<FirefoxPWABannerProps> = (props) => {
               {...{ class: CLASSES.firefoxBanner.media }}
             >
               <div {...{ class: CLASSES.firefoxBanner.iconWrap }}>
-                <Show when={browser() === "firefox"}>
-                  <Icon
-                    src="icon-[mdi--firefox]"
-                    width={40}
-                    height={40}
-                    {...{ class: CLASSES.firefoxBanner.browserIcon }}
-                  />
+                <Show when={browser() === "firefox" && props.icon}>
+                  {(icon) => (
+                    <Icon
+                      src={icon()}
+                      width={40}
+                      height={40}
+                      {...{ class: CLASSES.firefoxBanner.browserIcon }}
+                    />
+                  )}
                 </Show>
               </div>
 
diff --git a/src/components/immersive-landing/types.ts b/src/components/immersive-landing/types.ts
index 47c1dda5..c64f480f 100644
--- a/src/components/immersive-landing/types.ts
+++ b/src/components/immersive-landing/types.ts
@@ -138,6 +138,21 @@ export interface FirefoxPWABannerProps {
   extensionUrl?: string;
   storageKey?: string;
   texts?: FirefoxPWABannerTexts;
+  /**
+   * The browser mark shown beside the text. Omit it and the banner renders
+   * without one.
+   *
+   * A default lived here as `icon-[mdi--firefox]`, and it was the only reason
+   * this library needed a second Iconify set. Everything else it draws is
+   * `lucide`, which has no brand glyphs, so one banner in one optional
+   * component obliged every consumer to install all of `-json/mdi` --
+   * and a consumer who installed only `lucide` got build warnings and a blank
+   * space, which is what happened on crates.vip.
+   *
+   * Accepts what `Icon` accepts: an Iconify class such as
+   * `"icon-[mdi--firefox]"`, or an inline SVG element.
+   */
+  icon?: string | JSX.Element;
   onInstall?: () => void;
   onDismiss?: () => void;
 }
diff --git a/src/components/language-switcher/LanguageSwitcher.layout.tsx b/src/components/language-switcher/LanguageSwitcher.layout.tsx
index 64738b9e..ae327565 100644
--- a/src/components/language-switcher/LanguageSwitcher.layout.tsx
+++ b/src/components/language-switcher/LanguageSwitcher.layout.tsx
@@ -88,7 +88,7 @@ const LanguageSwitcher: Layout<
           when={!props.i18n.isLoading}
           fallback={
             <Icon
-              src="icon-[mdi--loading]"
+              src="icon-[lucide--loader-circle]"
               {...{ class: CLASSES.loadingIcon }}
               width={16}
               height={16}
diff --git a/src/components/table/MobileListView.layout.tsx b/src/components/table/MobileListView.layout.tsx
index a1b1e0f7..999a8c18 100644
--- a/src/components/table/MobileListView.layout.tsx
+++ b/src/components/table/MobileListView.layout.tsx
@@ -44,7 +44,7 @@ const MobileListView: Layout<typeof tableMobileListViewRecipe, MobileListViewPro
       <Empty>
         <Empty.Icon>
           <Icon
-            src={props.emptyIcon ?? "icon-[mdi--inbox-outline]"}
+            src={props.emptyIcon ?? "icon-[lucide--inbox]"}
             width={24}
             height={24}
           />
diff --git a/src/components/theme-color-picker/ThemeColorPicker.layout.tsx b/src/components/theme-color-picker/ThemeColorPicker.layout.tsx
index 1ab1d262..53e2e139 100644
--- a/src/components/theme-color-picker/ThemeColorPicker.layout.tsx
+++ b/src/components/theme-color-picker/ThemeColorPicker.layout.tsx
@@ -211,7 +211,7 @@ const ThemeColorPicker: Layout<typeof componentRecipe, ThemeColorPickerProps> =
         >
           {props.children ?? (
             <Icon
-              src="icon-[mdi--palette]"
+              src="icon-[lucide--palette]"
               width={16}
               height={16}
               {...{ class: store.themeColor() !== null ? CLASSES.iconActive : undefined }}
diff --git a/tests/components/single-icon-set.test.ts b/tests/components/single-icon-set.test.ts
new file mode 100644
index 00000000..eb92f59f
--- /dev/null
+++ b/tests/components/single-icon-set.test.ts
@@ -0,0 +1,69 @@
+import { describe, expect, it } from "bun:test";
+import { readdirSync, readFileSync, statSync } from "node:fs";
+import { join } from "node:path";
+
+/**
+ * Everything this library draws comes from one Iconify set.
+ *
+ * A consumer installs icon sets itself -- `@iconify-json/lucide` and so on --
+ * so every set the library reaches for is a set the consumer must know to
+ * install. Nothing states that requirement, and nothing fails loudly when it
+ * is unmet: the build prints `Cannot load icon set for "mdi"` among its
+ * warnings and the icon renders as empty space.
+ *
+ * That is what happened on crates.vip, which installed `lucide` because that
+ * is what the fleet uses. Five icons across `LanguageSwitcher`,
+ * `ThemeColorPicker`, `MobileListView` and the Firefox banner were `mdi`, and
+ * all five were blank. The library itself develops against `@iconify/json`,
+ * the whole collection, so it could never see this.
+ *
+ * The Firefox brand mark was the one icon with no lucide equivalent -- lucide
+ * has no brand glyphs. It is a prop now rather than a default, so a consumer
+ * who wants it supplies it and pays for the set, and everyone else pays
+ * nothing.
+ */
+const ALLOWED = "lucide";
+
+const SRC = join(import.meta.dir, "../../src");
+
+describe("icons come from one set", () => {
+  const files: string[] = [];
+  const walk = (dir: string) => {
+    for (const entry of readdirSync(dir)) {
+      const path = join(dir, entry);
+      if (statSync(path).isDirectory()) walk(path);
+      // Generated twins mirror their layout source, so a finding in one is the
+      // same finding in the other.
+      else if (/\.(ts|tsx|css)$/.test(entry) && !entry.includes(".generated."))
+        files.push(path);
+    }
+  };
+  walk(SRC);
+
+  // `icon-[set--name]` as it is written in a class or an `src`. Prose in a
+  // comment is not a reference, so the match has to be anchored to the
+  // delimiter a real one carries.
+  const references = new Map<string, string[]>();
+  for (const file of files) {
+    const text = readFileSync(file, "utf8");
+    for (const line of text.split("\n")) {
+      if (/^\s*(\*|\/\/)/.test(line)) continue;
+      for (const match of line.matchAll(/icon-\[([a-z0-9]+)--[a-z0-9-]+\]/g)) {
+        const set = match[1];
+        if (!references.has(set)) references.set(set, []);
+        references.get(set)?.push(file.replace(SRC, "src"));
+      }
+    }
+  }
+
+  it("finds icon references, so a broken walk cannot pass silently", () => {
+    expect(references.get(ALLOWED)?.length ?? 0).toBeGreaterThan(10);
+  });
+
+  it("uses no set other than the one consumers are told to install", () => {
+    const strays = [...references]
+      .filter(([set]) => set !== ALLOWED)
+      .map(([set, where]) => `${set}: ${[...new Set(where)].join(", ")}`);
+    expect(strays).toEqual([]);
+  });
+});