--- a/netwerk/dns/TRRService.cpp
+++ b/netwerk/dns/TRRService.cpp
@@ -11,16 +11,17 @@
 #include "TRR.h"
 #include "TRRService.h"
 
 #include "mozilla/Preferences.h"
 
 static const char kOpenCaptivePortalLoginEvent[] = "captive-portal-login";
 static const char kClearPrivateData[] = "clear-private-data";
 static const char kPurge[] = "browser:purge-session-history";
+static const char kDisableIpv6Pref[] = "network.dns.disableIPv6";
 
 #define TRR_PREF_PREFIX           "network.trr."
 #define TRR_PREF(x)               TRR_PREF_PREFIX x
 
 namespace mozilla {
 namespace net {
 
 #undef LOG
@@ -65,16 +66,17 @@ TRRService::Init()
     observerService->AddObserver(this, kOpenCaptivePortalLoginEvent, true);
     observerService->AddObserver(this, kClearPrivateData, true);
     observerService->AddObserver(this, kPurge, true);
   }
   nsCOMPtr<nsIPrefBranch> prefBranch;
   GetPrefBranch(getter_AddRefs(prefBranch));
   if (prefBranch) {
     prefBranch->AddObserver(TRR_PREF_PREFIX, this, true);
+    prefBranch->AddObserver(kDisableIpv6Pref, this, true);
   }
 
   ReadPrefs(NULL);
 
   gTRRService = this;
 
   LOG(("Initialized TRRService\n"));
   return NS_OK;
@@ -89,17 +91,19 @@ TRRService::Enabled()
   }
 
   if (mConfirmationState == CONFIRM_TRYING) {
     LOG(("TRRService::Enabled MaybeConfirm()\n"));
     MaybeConfirm();
   }
 
   if (mConfirmationState != CONFIRM_OK) {
-    LOG(("TRRService::Enabled mConfirmationState=%d\n", (int)mConfirmationState));
+    LOG(("TRRService::Enabled mConfirmationState=%d mCaptiveIsPassed=%d\n",
+         (int)mConfirmationState,
+         (int)mCaptiveIsPassed));
   }
 
   return (mConfirmationState == CONFIRM_OK);
 }
 
 void
 TRRService::GetPrefBranch(nsIPrefBranch **result)
 {
@@ -196,16 +200,22 @@ TRRService::ReadPrefs(const char *name)
     }
   }
   if (!name || !strcmp(name, TRR_PREF("early-AAAA"))) {
     bool tmp;
     if (NS_SUCCEEDED(Preferences::GetBool(TRR_PREF("early-AAAA"), &tmp))) {
       mEarlyAAAA = tmp;
     }
   }
+  if (!name || !strcmp(name, kDisableIpv6Pref)) {
+    bool tmp;
+    if (NS_SUCCEEDED(Preferences::GetBool(kDisableIpv6Pref, &tmp))) {
+      mDisableIPv6 = tmp;
+    }
+  }
 
   return NS_OK;
 }
 
 nsresult
 TRRService::GetURI(nsCString &result)
 {
   MutexAutoLock lock(mLock);

--- a/netwerk/dns/TRRService.h
+++ b/netwerk/dns/TRRService.h
@@ -32,16 +32,17 @@ public:
   nsresult Init();
   nsresult Start();
   bool Enabled();
 
   uint32_t Mode() { return mMode; }
   bool AllowRFC1918() { return mRfc1918; }
   bool UseGET() { return mUseGET; }
   bool EarlyAAAA() { return mEarlyAAAA; }
+  bool DisableIPv6() { return mDisableIPv6; }
   nsresult GetURI(nsCString &result);
   nsresult GetCredentials(nsCString &result);
   uint32_t GetRequestTimeout() { return mTRRTimeout; }
 
   LookupStatus CompleteLookup(nsHostRecord *, nsresult, mozilla::net::AddrInfo *, bool pb) override;
   void TRRBlacklist(const nsACString &host, bool privateBrowsing, bool aParentsToo);
   bool IsTRRBlacklisted(const nsACString &host, bool privateBrowsing, bool fullhost);
 
@@ -64,16 +65,17 @@ private:
   nsCString mConfirmationNS;
   nsCString mBootstrapAddr;
 
   Atomic<bool, Relaxed> mWaitForCaptive; // wait for the captive portal to say OK before using TRR
   Atomic<bool, Relaxed> mRfc1918; // okay with local IP addresses in DOH responses?
   Atomic<bool, Relaxed> mCaptiveIsPassed; // set when captive portal check is passed
   Atomic<bool, Relaxed> mUseGET; // do DOH using GET requests (instead of POST)
   Atomic<bool, Relaxed> mEarlyAAAA; // allow use of AAAA results before A is in
+  Atomic<bool, Relaxed> mDisableIPv6; // don't even try
 
   // TRR Blacklist storage
   RefPtr<DataStorage> mTRRBLStorage;
   Atomic<bool, Relaxed> mClearTRRBLStorage;
 
   enum ConfirmationState {
     CONFIRM_INIT = 0,
     CONFIRM_TRYING = 1,

--- a/netwerk/dns/nsHostResolver.cpp
+++ b/netwerk/dns/nsHostResolver.cpp
@@ -1129,16 +1129,19 @@ nsHostResolver::TrrLookup(nsHostRecord *
     if (pushedTRR) {
         rectype = pushedTRR->Type();
     }
     bool sendAgain;
 
     bool madeQuery = false;
     do {
         sendAgain = false;
+        if ((TRRTYPE_AAAA == rectype) && gTRRService && gTRRService->DisableIPv6()) {
+            break;
+        }
         LOG(("TRR Resolve %s type %d\n", rec->host.get(), (int)rectype));
         RefPtr<TRR> trr;
         MutexAutoLock trrlock(rec->mTrrLock);
         trr = pushedTRR ? pushedTRR : new TRR(this, rec, rectype);
         if (pushedTRR || NS_SUCCEEDED(NS_DispatchToMainThread(trr))) {
             rec->mResolving++;
             if (rectype == TRRTYPE_A) {
                 MOZ_ASSERT(!rec->mTrrA);