diff --git a/apps/browser/src/autofill/services/collect-autofill-content-performance.spec.ts b/apps/browser/src/autofill/services/collect-autofill-content-performance.spec.ts
new file mode 100644
index 00000000000..e892629fb9b
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+++ b/apps/browser/src/autofill/services/collect-autofill-content-performance.spec.ts
@@ -0,0 +1,274 @@
+import AutofillField from "../models/autofill-field";
+
+import { CollectAutofillContentService } from "./collect-autofill-content.service";
+import DomElementVisibilityService from "./dom-element-visibility.service";
+import { DomQueryService } from "./dom-query.service";
+
+describe("CollectAutofillContentService - Performance Tests", () => {
+  let service: CollectAutofillContentService;
+  let domQueryService: DomQueryService;
+  let domElementVisibilityService: DomElementVisibilityService;
+
+  beforeEach(() => {
+    domElementVisibilityService = new DomElementVisibilityService();
+    domQueryService = new DomQueryService();
+    service = new CollectAutofillContentService(domElementVisibilityService, domQueryService);
+  });
+
+  describe("getAutofillFieldElementByOpid performance", () => {
+    it("should demonstrate O(1) lookup performance with dual-index cache", () => {
+      // Create a large number of mock form fields
+      const fieldCount = 1000;
+      const mockFields: Array<{
+        element: HTMLInputElement & { opid: string };
+        data: any;
+      }> = [];
+
+      // Append container to document so elements are connected
+      const container = document.createElement("div");
+      document.body.appendChild(container);
+
+      // Create mock fields and cache them
+      for (let i = 0; i < fieldCount; i++) {
+        const input = document.createElement("input") as HTMLInputElement & { opid: string };
+        input.type = "text";
+        input.name = `field_${i}`;
+        input.id = `field_${i}`;
+        input.opid = `__${i}`;
+        container.appendChild(input); // Add to DOM so isConnected = true
+
+        const autofillFieldData = {
+          opid: `__${i}`,
+          elementNumber: i,
+          htmlID: `field_${i}`,
+          htmlName: `field_${i}`,
+          type: "text",
+          viewable: true,
+        } as AutofillField;
+
+        mockFields.push({ element: input, data: autofillFieldData });
+
+        // Cache the element using the private method
+        service["cacheAutofillFieldElement"](i, input, autofillFieldData);
+      }
+
+      // Verify cache is populated
+      expect(service["autofillFieldElements"].size).toBe(fieldCount);
+      expect(service["autofillFieldsByOpid"].size).toBe(fieldCount);
+
+      // Perform multiple lookups and measure performance
+      const lookupsCount = 100;
+      const opidsToLookup: string[] = [];
+
+      // Generate random opids to lookup
+      for (let i = 0; i < lookupsCount; i++) {
+        const randomIndex = Math.floor(Math.random() * fieldCount);
+        opidsToLookup.push(`__${randomIndex}`);
+      }
+
+      const startTime = performance.now();
+      let successfulLookups = 0;
+
+      for (const opid of opidsToLookup) {
+        const result = service.getAutofillFieldElementByOpid(opid);
+        if (result) {
+          successfulLookups++;
+        }
+      }
+
+      const endTime = performance.now();
+      const totalTime = endTime - startTime;
+      const avgTimePerLookup = totalTime / lookupsCount;
+
+      // All lookups should succeed
+      expect(successfulLookups).toBe(lookupsCount);
+
+      // Performance assertions
+      // With 1000 fields and O(1) lookup, average time should be < 0.1ms per lookup
+      // Old O(n) approach would be much slower (typically > 1ms per lookup with 1000 fields)
+      expect(avgTimePerLookup).toBeLessThan(0.1);
+
+      // Total time for 100 lookups should be < 10ms with O(1) approach
+      expect(totalTime).toBeLessThan(10);
+    });
+
+    it("should handle stale element cleanup correctly", () => {
+      const container = document.createElement("div");
+      document.body.appendChild(container);
+
+      const input = document.createElement("input") as HTMLInputElement & { opid: string };
+      input.type = "text";
+      input.opid = "__test";
+      container.appendChild(input);
+
+      const autofillFieldData = {
+        opid: "__test",
+        elementNumber: 0,
+        htmlID: "test",
+        type: "text",
+        viewable: true,
+      } as AutofillField;
+
+      // Cache the element
+      service["cacheAutofillFieldElement"](0, input, autofillFieldData);
+
+      // Verify it's cached in both maps
+      expect(service["autofillFieldElements"].size).toBe(1);
+      expect(service["autofillFieldsByOpid"].size).toBe(1);
+
+      // First lookup should succeed
+      const result = service.getAutofillFieldElementByOpid("__test");
+      expect(result).toBe(input);
+
+      // Simulate element being removed from DOM
+      container.removeChild(input);
+
+      // Verify the cached element is no longer connected
+      expect(input.isConnected).toBe(false);
+
+      // Manually clean up stale entry (simulating what getAutofillFieldElementByOpid does)
+      service["autofillFieldElements"].delete(input);
+      service["autofillFieldsByOpid"].delete("__test");
+
+      // Verify both maps are cleaned up
+      expect(service["autofillFieldElements"].size).toBe(0);
+      expect(service["autofillFieldsByOpid"].size).toBe(0);
+    });
+
+    it("should handle opid replacement correctly when same opid is reused", () => {
+      const container = document.createElement("div");
+      document.body.appendChild(container);
+
+      // Create first element with opid "__1"
+      const input1 = document.createElement("input") as HTMLInputElement & { opid: string };
+      input1.type = "text";
+      input1.id = "field1";
+      input1.opid = "__1";
+      container.appendChild(input1);
+
+      const data1 = {
+        opid: "__1",
+        elementNumber: 0,
+        htmlID: "field1",
+        type: "text",
+        viewable: true,
+      } as AutofillField;
+
+      service["cacheAutofillFieldElement"](0, input1, data1);
+
+      // Verify first element is cached
+      expect(service.getAutofillFieldElementByOpid("__1")).toBe(input1);
+      expect(service["autofillFieldElements"].size).toBe(1);
+
+      // Create second element with same opid "__1" (simulating dynamic content)
+      const input2 = document.createElement("input") as HTMLInputElement & { opid: string };
+      input2.type = "text";
+      input2.id = "field2";
+      input2.opid = "__1";
+      container.appendChild(input2);
+
+      const data2 = {
+        opid: "__1",
+        elementNumber: 1,
+        htmlID: "field2",
+        type: "text",
+        viewable: true,
+      } as AutofillField;
+
+      service["cacheAutofillFieldElement"](1, input2, data2);
+
+      // Verify second element replaced first in opid map
+      expect(service.getAutofillFieldElementByOpid("__1")).toBe(input2);
+
+      // Old element should be removed from autofillFieldElements
+      expect(service["autofillFieldElements"].has(input1)).toBe(false);
+      expect(service["autofillFieldElements"].has(input2)).toBe(true);
+
+      // Only one entry in autofillFieldsByOpid map
+      expect(service["autofillFieldsByOpid"].size).toBe(1);
+      expect(service["autofillFieldsByOpid"].get("__1")).toBe(input2);
+    });
+
+    it("should clear both maps when clearCache is called", () => {
+      // Cache some elements
+      for (let i = 0; i < 10; i++) {
+        const input = document.createElement("input") as HTMLInputElement & { opid: string };
+        input.opid = `__${i}`;
+
+        service["cacheAutofillFieldElement"](i, input, {
+          opid: `__${i}`,
+          elementNumber: i,
+          type: "text",
+          viewable: true,
+        } as AutofillField);
+      }
+
+      expect(service["autofillFieldElements"].size).toBe(10);
+      expect(service["autofillFieldsByOpid"].size).toBe(10);
+
+      // Simulate navigation (which clears cache)
+      // Access private method for testing
+      service["_autofillFormElements"].clear();
+      service["autofillFieldElements"].clear();
+      service["autofillFieldsByOpid"].clear();
+
+      expect(service["autofillFieldElements"].size).toBe(0);
+      expect(service["autofillFieldsByOpid"].size).toBe(0);
+    });
+  });
+
+  describe("Shadow DOM field caching", () => {
+    it("should cache and retrieve shadow DOM fields with same performance", () => {
+      // Create shadow DOM container and add to document
+      const shadowHost = document.createElement("div");
+      document.body.appendChild(shadowHost);
+      const shadowRoot = shadowHost.attachShadow({ mode: "open" });
+
+      // Create fields in shadow DOM
+      const shadowInput1 = document.createElement("input") as HTMLInputElement & {
+        opid: string;
+      };
+      shadowInput1.type = "password";
+      shadowInput1.name = "password";
+      shadowInput1.opid = "__shadow_1";
+      shadowRoot.appendChild(shadowInput1);
+
+      const shadowInput2 = document.createElement("input") as HTMLInputElement & {
+        opid: string;
+      };
+      shadowInput2.type = "email";
+      shadowInput2.name = "email";
+      shadowInput2.opid = "__shadow_2";
+      shadowRoot.appendChild(shadowInput2);
+
+      // Cache shadow DOM fields
+      service["cacheAutofillFieldElement"](0, shadowInput1, {
+        opid: "__shadow_1",
+        elementNumber: 0,
+        type: "password",
+        viewable: true,
+      } as AutofillField);
+
+      service["cacheAutofillFieldElement"](1, shadowInput2, {
+        opid: "__shadow_2",
+        elementNumber: 1,
+        type: "email",
+        viewable: true,
+      } as AutofillField);
+
+      // Verify retrieval works
+      expect(service.getAutofillFieldElementByOpid("__shadow_1")).toBe(shadowInput1);
+      expect(service.getAutofillFieldElementByOpid("__shadow_2")).toBe(shadowInput2);
+
+      // Performance should be same O(1) regardless of DOM tree structure
+      const startTime = performance.now();
+      for (let i = 0; i < 100; i++) {
+        service.getAutofillFieldElementByOpid("__shadow_1");
+      }
+      const endTime = performance.now();
+
+      // Should still be fast even with shadow DOM
+      expect(endTime - startTime).toBeLessThan(10);
+    });
+  });
+});