diff --git a/src/utils/multimap.ts b/src/utils/multimap.ts
index e32e1efbf2114..5c671fcc48c98 100644
--- a/src/utils/multimap.ts
+++ b/src/utils/multimap.ts
@@ -15,23 +15,23 @@
  */
 
 export class MultiMap<K, V> {
-  private _map: Map<K, Set<V>>;
+  private _map: Map<K, V[]>;
 
   constructor() {
-    this._map = new Map<K, Set<V>>();
+    this._map = new Map<K, V[]>();
   }
 
   set(key: K, value: V) {
-    let set = this._map.get(key);
-    if (!set) {
-      set = new Set<V>();
-      this._map.set(key, set);
+    let values = this._map.get(key);
+    if (!values) {
+      values = [];
+      this._map.set(key, values);
     }
-    set.add(value);
+    values.push(value);
   }
 
-  get(key: K): Set<V> {
-    return this._map.get(key) || new Set();
+  get(key: K): V[] {
+    return this._map.get(key) || [];
   }
 
   has(key: K): boolean {
@@ -39,28 +39,16 @@ export class MultiMap<K, V> {
   }
 
   hasValue(key: K, value: V): boolean {
-    const set = this._map.get(key);
-    if (!set)
+    const values = this._map.get(key);
+    if (!values)
       return false;
-    return set.has(value);
+    return values.includes(value);
   }
 
   get size(): number {
     return this._map.size;
   }
 
-  delete(key: K, value: V): boolean {
-    const values = this.get(key);
-    const result = values.delete(value);
-    if (!values.size)
-      this._map.delete(key);
-    return result;
-  }
-
-  deleteAll(key: K) {
-    this._map.delete(key);
-  }
-
   keys(): IterableIterator<K> {
     return this._map.keys();
   }
@@ -68,7 +56,7 @@ export class MultiMap<K, V> {
   values(): Iterable<V> {
     const result: V[] = [];
     for (const key of this.keys())
-      result.push(...Array.from(this.get(key)!));
+      result.push(...this.get(key));
     return result;
   }
 
diff --git a/tests/page/page-route.spec.ts b/tests/page/page-route.spec.ts
index 9aeaa0b716920..6b1e304902c1a 100644
--- a/tests/page/page-route.spec.ts
+++ b/tests/page/page-route.spec.ts
@@ -213,10 +213,14 @@ it('should pause intercepted fetch request until continue', async ({page, server
   expect(status).toBe(200);
 });
 
-it('should work with custom referer headers', async ({page, server}) => {
+it('should work with custom referer headers', async ({page, server, browserName}) => {
   await page.setExtraHTTPHeaders({ 'referer': server.EMPTY_PAGE });
   await page.route('**/*', route => {
-    expect(route.request().headers()['referer']).toBe(server.EMPTY_PAGE);
+    // See https://github.com/microsoft/playwright/issues/8999
+    if (browserName === 'chromium')
+      expect(route.request().headers()['referer']).toBe(server.EMPTY_PAGE + ', ' + server.EMPTY_PAGE);
+    else
+      expect(route.request().headers()['referer']).toBe(server.EMPTY_PAGE);
     route.continue();
   });
   const response = await page.goto(server.EMPTY_PAGE);
diff --git a/tests/page/page-set-extra-http-headers.spec.ts b/tests/page/page-set-extra-http-headers.spec.ts
index d03d6f16725b3..31702badc8f0c 100644
--- a/tests/page/page-set-extra-http-headers.spec.ts
+++ b/tests/page/page-set-extra-http-headers.spec.ts
@@ -60,3 +60,11 @@ it('should throw for non-string header values', async ({page}) => {
   const error2 = await page.context().setExtraHTTPHeaders({ 'foo': true }).catch(e => e);
   expect(error2.message).toContain('Expected value of header "foo" to be String, but "boolean" is found.');
 });
+
+it('should not duplicate referer header', async ({page, server, browserName}) => {
+  it.fail(browserName === 'chromium', 'Request has referer and Referer');
+  await page.setExtraHTTPHeaders({ 'referer': server.EMPTY_PAGE });
+  const response = await page.goto(server.EMPTY_PAGE);
+  expect(response.ok()).toBe(true);
+  expect(response.request().headers()['referer']).toBe(server.EMPTY_PAGE);
+});