Padlock caught in a filter net blocking a keyhole
Microsoft sign-in on a Mac can fail in weird ways when an ad blocker is on: infinite loading, “something went wrong,” blank white pages, or a CAPTCHA that never appears.

It’s usually not your password.

Most Microsoft sign-in flows rely on third-party domains, redirects, embedded scripts, and cookies. Ad blockers and privacy extensions sometimes treat those pieces like trackers and block them, which breaks the chain the login needs to complete.

Before you start changing a bunch of settings, it helps to understand what’s getting blocked.

1. Why ad blockers break Microsoft sign-in (what’s actually happening)

Modern Microsoft login isn’t just one page on one domain. It often involves multiple requests across domains like Microsoft account services, security challenges, and embedded resources.

Blocked connection in a multi-step sign-in flow diagram
An ad blocker can interrupt this in a few common ways:

  • Blocking “third-party” scripts that render the sign-in form, CAPTCHA, or “approve sign-in” prompt.
  • Blocking cookies or storage needed to keep your session between redirects (so you get bounced back to the start).
  • Blocking redirect or telemetry endpoints that Microsoft uses to verify the flow completed (even if you dislike telemetry, some endpoints are tied to authentication steps).
  • Upgrading or rewriting requests (some privacy tools route, strip, or modify requests in ways the sign-in page rejects).

If you only see the issue on one browser profile, one Mac, or one network, that’s another hint it’s a filter/extension rule rather than Microsoft being down.

Now let’s fix it with the smallest, safest changes first.

2. Confirm it’s the ad blocker (fast, reversible test)

Do a quick A/B test so you don’t chase the wrong cause.

  • Open a Private/Incognito window (many extensions are disabled there unless you allowed them).
  • Try signing in again.
  • If it works in Private/Incognito but fails normally, the issue is almost always extension rules, cookies, or cached site data.

If it still fails in Private/Incognito, temporarily disable the ad blocker for one minute and retest. Re-enable it right after.

  • If disabling the ad blocker makes sign-in work immediately, move on to whitelisting instead of leaving it off.

This is the point where you can fix it without “lowering privacy everywhere.”

3. Use a narrow allowlist for Microsoft sign-in (don’t turn protection off globally)

Shield and allowlist path passing through a filter gate
The goal is to allow only the minimum Microsoft domains needed for authentication, not every tracker on the page.

In your ad blocker, create a site exception (or “trusted site”) for the sign-in page you’re using. Then, if your blocker supports it, allow these only when needed:

  • login.live.com (common Microsoft account login)
  • login.microsoftonline.com (work/school accounts, Entra ID/Azure AD)
  • account.microsoft.com (account management, sometimes part of flow)

Tips that often matter:

  • If your blocker has a setting like “Block third-party scripts” or “Block third-party cookies” per-site, set it to Allow for the Microsoft sign-in domains only.
  • If you’re signing into Microsoft inside another app (like Teams, OneDrive, Outlook), also allow the sign-in domains above—those apps often open an embedded web view that uses the same endpoints.

If you’re not sure which domain is failing, many blockers have a “request log” or “blocked items” view. Look for blocked requests during sign-in and allow only what’s clearly tied to Microsoft authentication.

Still looping? That’s often cookies or cached login state.

4. Clear Microsoft sign-in cookies/site data (targeted, not a full browser wipe)

When a sign-in attempt is partially blocked, your browser can get stuck with half-created session cookies. You keep retrying, but the server sees an inconsistent state and sends you back.

  • In your browser settings, find Privacy → Cookies/Site Data (wording varies).
  • Search for and remove site data for: live.com, microsoftonline.com, microsoft.com.
  • Close the browser completely and reopen it.

If you rely on saved sessions elsewhere, avoid “Clear all history.” Targeting only Microsoft-related cookies is usually enough.

If you’re using Safari, there’s one more common snag.

5. On Safari: check cross-site tracking and content blockers for the sign-in domains

Safari’s privacy features can combine with an ad blocker to become “too strict” for some sign-in flows.

  • Open the Microsoft sign-in page.
  • In Safari, use the site-specific settings to ensure content blockers are not blocking that page.
  • If you have Prevent cross-site tracking enabled (good to keep on), try the allowlist approach first rather than turning it off globally.

If Safari continues to fail but another browser works, it’s often a Safari-specific content blocker rule or a corrupted Safari website data entry for Microsoft domains.

When none of the above works, it’s time to check for “stacked blockers.”

6. Look for stacked privacy tools (VPN filters, DNS blocking, multiple extensions)

On Mac, it’s easy to accidentally run two or three layers of blocking at once (for example: an ad blocker extension + a DNS blocker + a VPN with tracker blocking). Microsoft sign-in can break when one layer blocks a challenge endpoint and another blocks fallback.

  • Temporarily pause one layer at a time (not everything at once) and retest sign-in.
  • If you use a DNS-based blocker (like a filtered DNS profile), try switching to a standard DNS just long enough to complete sign-in.
  • If a VPN has an option like “block trackers/ads”, try disabling that feature (keeping the VPN on) to see if it’s the culprit.

If you identify the layer causing it, add an exception there and re-enable the rest.

Final thoughts

Microsoft sign-in failures caused by ad blockers are usually about blocked scripts, third-party cookies, or a corrupted half-finished session.

The safest fix is a narrow allowlist plus targeted cookie cleanup—so you can keep protection on everywhere else.