--- a/toolkit/components/url-classifier/ProtocolParser.cpp
+++ b/toolkit/components/url-classifier/ProtocolParser.cpp
@@ -180,16 +180,17 @@ ProtocolParserV2::AppendStream(const nsA
   }
   return NS_OK;
 }
 
 void
 ProtocolParserV2::End()
 {
   // Inbound data has already been processed in every AppendStream() call.
+  mTableUpdate = nullptr;
 }
 
 nsresult
 ProtocolParserV2::ProcessControl(bool* aDone)
 {
   nsresult rv;
 
   nsAutoCString line;
@@ -518,16 +519,17 @@ ProtocolParserV2::ProcessDigestChunk(con
     return ProcessDigestSub(aChunk);
   }
   return NS_ERROR_UNEXPECTED;
 }
 
 nsresult
 ProtocolParserV2::ProcessDigestAdd(const nsACString& aChunk)
 {
+  MOZ_ASSERT(mTableUpdate);
   // The ABNF format for add chunks is (HASH)+, where HASH is 32 bytes.
   MOZ_ASSERT(aChunk.Length() % 32 == 0,
              "Chunk length in bytes must be divisible by 4");
   uint32_t start = 0;
   while (start < aChunk.Length()) {
     Completion hash;
     hash.Assign(Substring(aChunk, start, COMPLETE_SIZE));
     start += COMPLETE_SIZE;
@@ -537,16 +539,17 @@ ProtocolParserV2::ProcessDigestAdd(const
     }
   }
   return NS_OK;
 }
 
 nsresult
 ProtocolParserV2::ProcessDigestSub(const nsACString& aChunk)
 {
+  MOZ_ASSERT(mTableUpdate);
   // The ABNF format for sub chunks is (ADDCHUNKNUM HASH)+, where ADDCHUNKNUM
   // is a 4 byte chunk number, and HASH is 32 bytes.
   MOZ_ASSERT(aChunk.Length() % 36 == 0,
              "Chunk length in bytes must be divisible by 36");
   uint32_t start = 0;
   while (start < aChunk.Length()) {
     // Read ADDCHUNKNUM
     const nsACString& addChunkStr = Substring(aChunk, start, 4);
@@ -568,16 +571,17 @@ ProtocolParserV2::ProcessDigestSub(const
   }
   return NS_OK;
 }
 
 nsresult
 ProtocolParserV2::ProcessHostAdd(const Prefix& aDomain, uint8_t aNumEntries,
                                const nsACString& aChunk, uint32_t* aStart)
 {
+  MOZ_ASSERT(mTableUpdate);
   NS_ASSERTION(mChunkState.hashSize == PREFIX_SIZE,
                "ProcessHostAdd should only be called for prefix hashes.");
 
   if (aNumEntries == 0) {
     nsresult rv = mTableUpdate->NewAddPrefix(mChunkState.num, aDomain);
     if (NS_FAILED(rv)) {
       return rv;
     }
@@ -602,16 +606,17 @@ ProtocolParserV2::ProcessHostAdd(const P
 
   return NS_OK;
 }
 
 nsresult
 ProtocolParserV2::ProcessHostSub(const Prefix& aDomain, uint8_t aNumEntries,
                                const nsACString& aChunk, uint32_t *aStart)
 {
+  MOZ_ASSERT(mTableUpdate);
   NS_ASSERTION(mChunkState.hashSize == PREFIX_SIZE,
                "ProcessHostSub should only be called for prefix hashes.");
 
   if (aNumEntries == 0) {
     if ((*aStart) + 4 > aChunk.Length()) {
       NS_WARNING("Received a zero-entry sub chunk without an associated add.");
       return NS_ERROR_FAILURE;
     }
@@ -657,16 +662,17 @@ ProtocolParserV2::ProcessHostSub(const P
 
   return NS_OK;
 }
 
 nsresult
 ProtocolParserV2::ProcessHostAddComplete(uint8_t aNumEntries,
                                        const nsACString& aChunk, uint32_t* aStart)
 {
+  MOZ_ASSERT(mTableUpdate);
   NS_ASSERTION(mChunkState.hashSize == COMPLETE_SIZE,
                "ProcessHostAddComplete should only be called for complete hashes.");
 
   if (aNumEntries == 0) {
     // this is totally comprehensible.
     // My sarcasm detector is going off!
     NS_WARNING("Expected > 0 entries for a 32-byte hash add.");
     return NS_OK;
@@ -689,16 +695,17 @@ ProtocolParserV2::ProcessHostAddComplete
 
   return NS_OK;
 }
 
 nsresult
 ProtocolParserV2::ProcessHostSubComplete(uint8_t aNumEntries,
                                        const nsACString& aChunk, uint32_t* aStart)
 {
+  MOZ_ASSERT(mTableUpdate);
   NS_ASSERTION(mChunkState.hashSize == COMPLETE_SIZE,
                "ProcessHostSubComplete should only be called for complete hashes.");
 
   if (aNumEntries == 0) {
     // this is totally comprehensible.
     NS_WARNING("Expected > 0 entries for a 32-byte hash sub.");
     return NS_OK;
   }