diff --git a/netwerk/protocol/http/Http2Push.h b/netwerk/protocol/http/Http2Push.h
index 692b644b2ddf..c43d813b8cc9 100644
--- a/netwerk/protocol/http/Http2Push.h
+++ b/netwerk/protocol/http/Http2Push.h
@@ -113,6 +113,7 @@ public:
 
 private:
   virtual ~Http2PushTransactionBuffer();
+  uint64_t Available();
 
   const static uint32_t kDefaultBufferSize = 4096;
 
diff --git a/netwerk/protocol/http/Http2Session.cpp b/netwerk/protocol/http/Http2Session.cpp
index 754be31b172f..6bb805c1e294 100644
--- a/netwerk/protocol/http/Http2Session.cpp
+++ b/netwerk/protocol/http/Http2Session.cpp
@@ -4035,13 +4035,6 @@ Http2Session::SetDNSWasRefreshed()
   MOZ_ASSERT(false, "Http2Session::SetDNSWasRefreshed()");
 }
 
-uint64_t
-Http2Session::Available()
-{
-  MOZ_ASSERT(false, "Http2Session::Available()");
-  return 0;
-}
-
 nsHttpRequestHead *
 Http2Session::RequestHead()
 {
diff --git a/netwerk/protocol/http/NullHttpTransaction.cpp b/netwerk/protocol/http/NullHttpTransaction.cpp
index ddbdf1c3311f..8665ee7ca617 100644
--- a/netwerk/protocol/http/NullHttpTransaction.cpp
+++ b/netwerk/protocol/http/NullHttpTransaction.cpp
@@ -208,12 +208,6 @@ NullHttpTransaction::SetDNSWasRefreshed()
   mCapsToClear |= NS_HTTP_REFRESH_DNS;
 }
 
-uint64_t
-NullHttpTransaction::Available()
-{
-  return 0;
-}
-
 nsresult
 NullHttpTransaction::ReadSegments(nsAHttpSegmentReader *reader,
                                   uint32_t count, uint32_t *countRead)
diff --git a/netwerk/protocol/http/TunnelUtils.cpp b/netwerk/protocol/http/TunnelUtils.cpp
index df853fb01b8c..5dbcaec5d2c9 100644
--- a/netwerk/protocol/http/TunnelUtils.cpp
+++ b/netwerk/protocol/http/TunnelUtils.cpp
@@ -616,16 +616,6 @@ TLSFilterTransaction::SetDNSWasRefreshed()
   mTransaction->SetDNSWasRefreshed();
 }
 
-uint64_t
-TLSFilterTransaction::Available()
-{
-  if (!mTransaction) {
-    return 0;
-  }
-
-  return mTransaction->Available();
-}
-
 void
 TLSFilterTransaction::SetProxyConnectFailed()
 {
diff --git a/netwerk/protocol/http/nsAHttpTransaction.h b/netwerk/protocol/http/nsAHttpTransaction.h
index d167c541caec..8943e0cb0cee 100644
--- a/netwerk/protocol/http/nsAHttpTransaction.h
+++ b/netwerk/protocol/http/nsAHttpTransaction.h
@@ -64,9 +64,6 @@ public:
     // called to notify that a requested DNS cache entry was refreshed.
     virtual void     SetDNSWasRefreshed() = 0;
 
-    // called to find out how much request data is available for writing.
-    virtual uint64_t Available() = 0;
-
     // called to read request data from the transaction.
     virtual MOZ_MUST_USE nsresult ReadSegments(nsAHttpSegmentReader *reader,
                                                uint32_t count,
@@ -214,7 +211,6 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsAHttpTransaction, NS_AHTTPTRANSACTION_IID)
     nsresult Status() override; \
     uint32_t Caps() override;   \
     void     SetDNSWasRefreshed() override; \
-    uint64_t Available() override; \
     virtual MOZ_MUST_USE nsresult ReadSegments(nsAHttpSegmentReader *, uint32_t, uint32_t *) override; \
     virtual MOZ_MUST_USE nsresult WriteSegments(nsAHttpSegmentWriter *, uint32_t, uint32_t *) override; \
     virtual void Close(nsresult reason) override;                                \
diff --git a/netwerk/protocol/http/nsHttpTransaction.cpp b/netwerk/protocol/http/nsHttpTransaction.cpp
index cbf886b8950c..ace5583a0c6a 100644
--- a/netwerk/protocol/http/nsHttpTransaction.cpp
+++ b/netwerk/protocol/http/nsHttpTransaction.cpp
@@ -652,15 +652,6 @@ nsHttpTransaction::SetDNSWasRefreshed()
     mCapsToClear |= NS_HTTP_REFRESH_DNS;
 }
 
-uint64_t
-nsHttpTransaction::Available()
-{
-    uint64_t size;
-    if (NS_FAILED(mRequestStream->Available(&size)))
-        size = 0;
-    return size;
-}
-
 nsresult
 nsHttpTransaction::ReadRequestSegment(nsIInputStream *stream,
                                       void *closure,