diff --git a/floxis-backport-kit/INTEGRATION.md b/floxis-backport-kit/INTEGRATION.md
index b01e2bc4f97..9e824af07b6 100644
--- a/floxis-backport-kit/INTEGRATION.md
+++ b/floxis-backport-kit/INTEGRATION.md
@@ -113,7 +113,23 @@ pbjs.setConfig({
 Floxis syncs entirely, exclude `floxis` from both `iframe` and `image`; `userSync.syncEnabled: false`
 disables syncs for all bidders.
 
-## 5. Verification & troubleshooting
+## 5. Enable first-party fallback id (recommended)
+
+The adapter mints a random UUID in the publisher's own page context (`localStorage` + cookie, scoped to the publisher's origin) and sends it at `user.ext.floxisId`. This is an identity-of-last-resort for Safari, Firefox and other browsers where the Floxis third-party cookie (`__fxId`) is blocked — it does not affect Chrome/Edge, where the third-party cookie takes precedence on the backend.
+
+Since Prebid.js 7.x, bidder-level storage access is **denied by default**. Without the opt-in below, no id is generated and no storage is touched — a safe no-op, not an error. To enable it:
+
+```javascript
+pbjs.bidderSettings = {
+  floxis: {
+    storageAllowed: true
+  }
+};
+```
+
+This is scoped to the Floxis bidder only and does not affect storage permissions for your other SSPs. Storage access is further gated by Prebid.js core's `deviceAccess` config and GDPR purpose-1 consent under Floxis's registered gvlid (1609).
+
+## 6. Verification & troubleshooting
 
 - **Enable debugging:** `pbjs.setConfig({ debug: true })` and watch the console.
 - **Module check:** confirm `floxisBidAdapter` appears in `pbjs.installedModules`.
diff --git a/floxis-backport-kit/modules/floxisBidAdapter.js b/floxis-backport-kit/modules/floxisBidAdapter.js
index bde6cbe1d11..fe70a0c4a67 100644
--- a/floxis-backport-kit/modules/floxisBidAdapter.js
+++ b/floxis-backport-kit/modules/floxisBidAdapter.js
@@ -1,8 +1,9 @@
 import { registerBidder } from '../src/adapters/bidderFactory.js';
 import { BANNER, NATIVE, VIDEO } from '../src/mediaTypes.js';
 import { ortbConverter } from '../libraries/ortbConverter/converter.js';
-import { triggerPixel, mergeDeep, replaceAuctionPrice } from '../src/utils.js';
+import { triggerPixel, mergeDeep, replaceAuctionPrice, generateUUID } from '../src/utils.js';
 import { politeTriggerPixel } from '../libraries/floxisUtils/politePixel.js';
+import { getStorageManager } from '../src/storageManager.js';
 
 const BIDDER_CODE = 'floxis';
 const GVLID = 1609;
@@ -12,6 +13,11 @@ const DEFAULT_NET_REVENUE = true;
 const DEFAULT_REGION = 'us-e';
 const DEFAULT_PARTNER = BIDDER_CODE;
 const SYNC_PATH = '/sync';
+const FLOXIS_ID_KEY = 'flx_uid';
+const FLOXIS_ID_COOKIE_EXP = 2592000000; // 30 days
+const UUID_LENGTH = 36;
+
+export const storage = getStorageManager({ bidderCode: BIDDER_CODE });
 // Server-echo user-sync: the /pbjs response carries seat + region in this header (on bid and no-bid
 // alike), so getUserSyncs derives sync targets from serverResponses statelessly — no module state that
 // could leak across concurrent auctions. Absent header (older backend) => no sync, a safe no-op.
@@ -89,6 +95,40 @@ function normalizeBidParams(params = {}) {
   };
 }
 
+function isValidFloxisId(id) {
+  return typeof id === 'string' && id.length === UUID_LENGTH;
+}
+
+// Neither store available => null, not a freshly minted id we can't persist (would defeat stability).
+function getOrCreateFloxisId() {
+  if (typeof window === 'undefined') return null;
+  try {
+    const localOk = storage.localStorageIsEnabled();
+    const cookieOk = storage.cookiesAreEnabled();
+    if (!localOk && !cookieOk) return null;
+
+    let id = localOk ? storage.getDataFromLocalStorage(FLOXIS_ID_KEY) : null;
+    if (!isValidFloxisId(id) && cookieOk) {
+      id = storage.getCookie(FLOXIS_ID_KEY);
+    }
+    if (!isValidFloxisId(id)) {
+      id = generateUUID();
+    }
+
+    if (localOk) {
+      storage.setDataInLocalStorage(FLOXIS_ID_KEY, id);
+    }
+    if (cookieOk) {
+      const expires = new Date(Date.now() + FLOXIS_ID_COOKIE_EXP).toUTCString();
+      storage.setCookie(FLOXIS_ID_KEY, id, expires);
+    }
+
+    return id;
+  } catch (e) {
+    return null;
+  }
+}
+
 // Parse the server-echoed sync header (`seat=<seat>&region=<label>`) into a sync target. Returns null
 // for an absent or malformed header so a response without it simply contributes no sync.
 function parseSyncHeader(headerValue) {
@@ -152,6 +192,12 @@ const CONVERTER = ortbConverter({
         }
       }
     });
+    if (!req.user?.ext?.floxisId) {
+      const floxisId = getOrCreateFloxisId();
+      if (floxisId) {
+        mergeDeep(req, { user: { ext: { floxisId } } });
+      }
+    }
     return req;
   },
   bidResponse(buildBidResponse, bid, context) {
diff --git a/floxis-backport-kit/modules/floxisBidAdapter.md b/floxis-backport-kit/modules/floxisBidAdapter.md
index 895feadeb09..a77f995f0e8 100644
--- a/floxis-backport-kit/modules/floxisBidAdapter.md
+++ b/floxis-backport-kit/modules/floxisBidAdapter.md
@@ -15,6 +15,7 @@ The Floxis Bid Adapter enables integration with the Floxis programmatic advertis
 - OpenRTB 2.x compliant
 - Privacy signal forwarding (GDPR/TCF, USP, GPP, COPPA) via Prebid.js core
 - User identity (User ID / `eids`) and supply chain (`schain`) passthrough
+- First-party fallback id for cookieless browsers (`user.ext.floxisId`)
 - Prebid.js Floors Module support (plus a static `bidFloor` param fallback)
 - User sync (iframe and pixel cookie matching)
 
@@ -29,6 +30,22 @@ The Floxis Bid Adapter supports the Prebid.js [Floors Module](https://docs.prebi
 ## User Identity & Supply Chain
 `user.ext.eids` from the Prebid [User ID module](https://docs.prebid.org/dev-docs/modules/userId.html) and `source.ext.schain` (set via `pbjs.setConfig({ schain })` or `ortb2`) are forwarded automatically through first-party-data passthrough — no adapter-specific configuration is required.
 
+## First-Party Fallback Id
+Floxis's primary identity signal, the `__fxId` cookie set on `.floxis.tech`, is a third-party cookie relative to the publisher and is blocked by Safari, Firefox and other ITP/ETP browsers. To keep an identity-of-last-resort in those browsers, the adapter mints a random v4 UUID **in the publisher's own page context** (first-party) and places it at `user.ext.floxisId` in the OpenRTB request.
+
+- **Storage & scope**: the id is persisted via `localStorage` (preferred) and a cookie, both scoped to the *publisher's own origin* — it is per-publisher, not cross-site, and is never shared between different sites running the adapter. Cookie lifetime is ~30 days; the id is regenerated if the stored value is not a well-formed 36-character UUID.
+- **Priority on the backend**: the client id is a fallback only. Floxis's backend applies `processedCookieUserId (the __fxId cookie) .orElse(clientFloxisId) .orElse(existing user.id)` — when the `__fxId` cookie is present (e.g. Chrome/Edge), behavior is unchanged and the client id is ignored.
+- **Consent**: storage access goes through Prebid.js core's `storageManager`, gated by the standard `deviceAccess` config and GDPR purpose-1 consent under Floxis's registered `gvlid` (1609) — the adapter adds no bespoke consent logic. If storage access is disallowed, no id is generated or sent, and the auction is unaffected.
+- **Publisher opt-in required**: since Prebid.js 7.x, bidder-level storage access is denied by default and must be explicitly granted per bidder — without it, no `floxisId` is ever generated (a safe no-op, not an error). Enable it via:
+```js
+// https://docs.prebid.org/dev-docs/publisher-api-reference/bidderSettings.html
+pbjs.bidderSettings = {
+    floxis: {
+        storageAllowed: true
+    }
+}
+```
+
 ## Privacy
 GDPR/TCF, US Privacy, GPP and COPPA signals are handled by Prebid.js core and automatically included in the OpenRTB request; consent strings are also appended to user-sync calls. Floxis is registered with IAB Europe TCF as Vendor ID **1609**, declared via the adapter's `gvlid`.
 
diff --git a/floxis-backport-kit/test/spec/modules/floxisBidAdapter_spec.js b/floxis-backport-kit/test/spec/modules/floxisBidAdapter_spec.js
index d8ac0977ffc..992e5e4c213 100644
--- a/floxis-backport-kit/test/spec/modules/floxisBidAdapter_spec.js
+++ b/floxis-backport-kit/test/spec/modules/floxisBidAdapter_spec.js
@@ -1,6 +1,6 @@
 import { expect } from 'chai';
 import sinon from 'sinon';
-import { spec } from 'modules/floxisBidAdapter.js';
+import { spec, storage } from 'modules/floxisBidAdapter.js';
 import { BANNER, NATIVE, VIDEO } from 'src/mediaTypes.js';
 import * as utils from 'src/utils.js';
 import * as floxisPolitePixel from '../../../libraries/floxisUtils/politePixel.js';
@@ -387,6 +387,144 @@ describe('floxisBidAdapter', function () {
         expect(data.cur).to.deep.equal(['USD']);
       });
     });
+
+    describe('First-party fallback id (user.ext.floxisId)', function () {
+      const STUBBED_UUID = '11111111-1111-4111-8111-111111111111';
+      const STORED_UUID = '22222222-2222-4222-8222-222222222222';
+      // ortb2.id avoids the core request processor's own generateUUID() call for req.id, so the stub's call count reflects only the floxisId logic.
+      const floxisIdBidderRequest = { ...bidderRequest, ortb2: { id: 'fixed-request-id' } };
+      let localStorageIsEnabledStub, cookiesAreEnabledStub;
+      let getDataFromLocalStorageStub, getCookieStub;
+      let setDataInLocalStorageStub, setCookieStub;
+      let generateUUIDStub;
+
+      beforeEach(function () {
+        localStorageIsEnabledStub = sinon.stub(storage, 'localStorageIsEnabled');
+        cookiesAreEnabledStub = sinon.stub(storage, 'cookiesAreEnabled');
+        getDataFromLocalStorageStub = sinon.stub(storage, 'getDataFromLocalStorage');
+        getCookieStub = sinon.stub(storage, 'getCookie');
+        setDataInLocalStorageStub = sinon.stub(storage, 'setDataInLocalStorage');
+        setCookieStub = sinon.stub(storage, 'setCookie');
+        generateUUIDStub = sinon.stub(utils, 'generateUUID').returns(STUBBED_UUID);
+      });
+
+      afterEach(function () {
+        localStorageIsEnabledStub.restore();
+        cookiesAreEnabledStub.restore();
+        getDataFromLocalStorageStub.restore();
+        getCookieStub.restore();
+        setDataInLocalStorageStub.restore();
+        setCookieStub.restore();
+        generateUUIDStub.restore();
+      });
+
+      it('mints and persists a new id when none is stored', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.returns(null);
+        getCookieStub.returns(null);
+
+        const data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+
+        expect(data.user.ext.floxisId).to.equal(STUBBED_UUID);
+        expect(generateUUIDStub.calledOnce).to.be.true;
+        expect(setDataInLocalStorageStub.calledWith('flx_uid', STUBBED_UUID)).to.be.true;
+        expect(setCookieStub.calledWith('flx_uid', STUBBED_UUID)).to.be.true;
+      });
+
+      it('reuses a valid stored id without regenerating it', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.returns(STORED_UUID);
+
+        const data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+
+        expect(data.user.ext.floxisId).to.equal(STORED_UUID);
+        expect(generateUUIDStub.called).to.be.false;
+      });
+
+      it('falls back to the cookie when localStorage has no stored value', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.returns(null);
+        getCookieStub.returns(STORED_UUID);
+
+        const data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+
+        expect(data.user.ext.floxisId).to.equal(STORED_UUID);
+        expect(generateUUIDStub.called).to.be.false;
+      });
+
+      it('regenerates the id when the stored value is a malformed UUID', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.returns('not-a-uuid');
+        getCookieStub.returns('also-not-a-uuid');
+
+        const data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+
+        expect(data.user.ext.floxisId).to.equal(STUBBED_UUID);
+        expect(generateUUIDStub.calledOnce).to.be.true;
+        expect(setDataInLocalStorageStub.calledWith('flx_uid', STUBBED_UUID)).to.be.true;
+      });
+
+      it('sends no id and does not throw when storage is disallowed', function () {
+        localStorageIsEnabledStub.returns(false);
+        cookiesAreEnabledStub.returns(false);
+
+        let data;
+        expect(function () {
+          data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+        }).to.not.throw();
+
+        expect(data.user?.ext?.floxisId).to.be.undefined;
+        expect(setDataInLocalStorageStub.called).to.be.false;
+        expect(setCookieStub.called).to.be.false;
+      });
+
+      it('sends no id and does not throw when a storage accessor throws', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.throws(new Error('storage access error'));
+
+        let data;
+        expect(function () {
+          data = spec.buildRequests([validBannerBid], floxisIdBidderRequest)[0].data;
+        }).to.not.throw();
+
+        expect(data.user?.ext?.floxisId).to.be.undefined;
+      });
+
+      it('does not clobber other user.ext fields set via ortb2 FPD', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+        getDataFromLocalStorageStub.returns(null);
+        getCookieStub.returns(null);
+
+        const ortb2BidderRequest = {
+          ...floxisIdBidderRequest,
+          ortb2: { ...floxisIdBidderRequest.ortb2, user: { ext: { consent: 'consent-string-123' } } }
+        };
+        const data = spec.buildRequests([validBannerBid], ortb2BidderRequest)[0].data;
+
+        expect(data.user.ext.consent).to.equal('consent-string-123');
+        expect(data.user.ext.floxisId).to.equal(STUBBED_UUID);
+      });
+
+      it('does not overwrite an existing user.ext.floxisId', function () {
+        localStorageIsEnabledStub.returns(true);
+        cookiesAreEnabledStub.returns(true);
+
+        const ortb2BidderRequest = {
+          ...floxisIdBidderRequest,
+          ortb2: { ...floxisIdBidderRequest.ortb2, user: { ext: { floxisId: STORED_UUID } } }
+        };
+        const data = spec.buildRequests([validBannerBid], ortb2BidderRequest)[0].data;
+
+        expect(data.user.ext.floxisId).to.equal(STORED_UUID);
+        expect(generateUUIDStub.called).to.be.false;
+      });
+    });
   });
 
   describe('interpretResponse', function () {