When a VPN is enabled, Firefox on Mac can suddenly feel “half online”: some sites load, others time out, logins fail, or pages spin forever. The good news is you can usually narrow it down in a few minutes with a quick checklist, then only go deeper if needed.

Shielded network cable kink causing blocked connection

Start with the fast checks below, in order.

Quick checklist (2–5 minutes)

  • Try one site that fails + one that works (so you can tell if changes help).
  • Toggle VPN off/on, then reload the same page in Firefox.
  • Try a Private Window (File → New Private Window) to bypass some cached state.
  • Switch VPN server/region once (same country first, then another).
  • Disable “Proxy” settings if you don’t use one (macOS and Firefox checks below).
  • Test another browser (Safari). If Safari also fails, it’s probably VPN/DNS rather than Firefox-only.

If the quick checklist didn’t fix it, work through the steps below.

1. Confirm whether it’s Firefox-only or VPN-wide

Before changing lots of settings, isolate the scope.

  • With VPN ON: try the failing site in Safari.
  • With VPN OFF: try the same site in Firefox.

What the results usually mean:

  • Fails in all browsers only when VPN is ON → VPN server/DNS/routing issue is most likely.
  • Fails only in Firefox (VPN ON) → Firefox proxy/DNS-over-HTTPS/caching is a common cause.

Two tiles with checks showing scope test across apps

2. Switch VPN protocol or server (the most common “real” fix)

Many timeouts come from the VPN route you’re on, not Firefox. Two small changes often fix it without touching browser settings.

  • Change server/location: pick a nearby server first, then one in another region if needed.
  • Change VPN protocol (in your VPN app): try WireGuard ↔ OpenVPN ↔ IKEv2 (names vary by provider).

After each change, fully reload the page (Shift + Reload button) and retry the same site you used in the checklist.

3. Check macOS Proxy settings (VPN apps sometimes set these)

If macOS has an unexpected proxy enabled, Firefox may “look connected” but requests never reach the site.

  • Open System Settings → Network.
  • Select your active connection (Wi‑Fi or Ethernet) → Details.
  • Open the Proxies tab.
  • Turn off proxies you don’t intentionally use (common ones: Web Proxy (HTTP), Secure Web Proxy (HTTPS), SOCKS Proxy).

Then quit and reopen Firefox and test again with the VPN on.

4. Set Firefox to “No proxy” (unless you explicitly need one)

Firefox has its own proxy setting, which can conflict with VPN networking.

  • In Firefox: Settings → General.
  • Scroll to Network Settings → Settings…
  • Select No proxy (or Use system proxy settings if your organization requires it).
  • Click OK, then reload the failing site.

If you’re on a work/school network that requires a proxy, choose “Use system proxy settings” and confirm the correct proxy details in macOS instead of leaving Firefox on a manual proxy.

5. Toggle DNS-over-HTTPS in Firefox (can clash with VPN DNS)

VPNs often want to control DNS to prevent leaks and to reach internal or region-specific domains. Firefox’s DNS-over-HTTPS (DoH) can override that and cause odd failures (timeouts, CAPTCHA loops, “site can’t be reached”).

DNS globe icon connected to a lock toggle switch

  • In Firefox: Settings → Privacy & Security.
  • Scroll to DNS over HTTPS.
  • Try switching it Off (or from “Increased/Max Protection” to “Default”).

Retest with the VPN on. If it fixes the issue, leave DoH off while using the VPN (or use your VPN provider’s recommended DNS/DoH configuration).

6. Clear network-related state (without nuking everything)

If the VPN recently changed regions or you toggled settings a lot, Firefox can hang onto stale connection info.

  • Hard reload: hold Shift and click Reload.
  • Clear only site data for the problem domain: Settings → Privacy & Security → Cookies and Site Data → Manage Data… → search the site → Remove Selected.
  • Disable extensions temporarily (especially ad blockers, privacy tools, VPN/proxy add-ons): open Add-ons and themes → Extensions → toggle off, then test.

If an extension is the cause, turn them back on one-by-one to find the offender.

Final thoughts

With VPN issues on Firefox for Mac, the fastest wins are usually: switch VPN server/protocol, remove unexpected proxies, and align Firefox DNS-over-HTTPS with your VPN’s DNS.

If nothing changes across browsers, it’s likely the VPN route itself—try a different region or contact your VPN provider with the failing domains and timestamp.