diff --git a/layout/style/nsLayoutStylesheetCache.cpp b/layout/style/nsLayoutStylesheetCache.cpp
index a3beca5f809..6acb833d3a9 100644
--- a/layout/style/nsLayoutStylesheetCache.cpp
+++ b/layout/style/nsLayoutStylesheetCache.cpp
@@ -27,6 +27,7 @@
 #include "nsIChromeRegistry.h"
 #include "nsISimpleEnumerator.h"
 #include "nsISubstitutingProtocolHandler.h"
+#include "zlib.h"
 #endif
 
 using namespace mozilla;
@@ -469,6 +470,30 @@ nsLayoutStylesheetCache::LoadSheetFile(nsIFile* aFile,
 }
 
 #ifdef MOZ_CRASHREPORTER
+static inline nsresult
+ComputeCRC32(nsIFile* aFile, uint32_t* aResult)
+{
+  PRFileDesc* fd;
+  nsresult rv = aFile->OpenNSPRFileDesc(PR_RDONLY, 0, &fd);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t crc = crc32(0, nullptr, 0);
+
+  unsigned char buf[512];
+  int32_t n;
+  while ((n = PR_Read(fd, buf, sizeof(buf))) > 0) {
+    crc = crc32(crc, buf, n);
+  }
+  PR_Close(fd);
+
+  if (n < 0) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aResult = crc;
+  return NS_OK;
+}
+
 static void
 ListInterestingFiles(nsString& aAnnotation, nsIFile* aFile,
                      const nsTArray<nsString>& aInterestingFilenames)
@@ -488,7 +513,14 @@ ListInterestingFiles(nsString& aAnnotation, nsIFile* aFile,
       } else {
         aAnnotation.AppendLiteral("???");
       }
-      aAnnotation.AppendLiteral(" bytes)\n");
+      aAnnotation.AppendLiteral(" bytes, crc32 = ");
+      uint32_t crc;
+      nsresult rv = ComputeCRC32(aFile, &crc);
+      if (NS_SUCCEEDED(rv)) {
+        aAnnotation.AppendPrintf("0x%08x)\n", crc);
+      } else {
+        aAnnotation.AppendPrintf("error 0x%08x)\n", uint32_t(rv));
+      }
       return;
     }
   }
@@ -553,6 +585,14 @@ AnnotateCrashReport(nsIURI* aURI)
   annotation.Append(NS_ConvertUTF8toUTF16(spec).get());
   annotation.Append('\n');
 
+  annotation.AppendLiteral("NS_ERROR_FILE_CORRUPTION reason: ");
+  if (nsZipArchive::sFileCorruptedReason) {
+    annotation.Append(NS_ConvertUTF8toUTF16(nsZipArchive::sFileCorruptedReason).get());
+    annotation.Append('\n');
+  } else {
+    annotation.AppendLiteral("(none)\n");
+  }
+
   // The jar: or file: URL that the sheet's resource: or chrome: URL
   // resolves to.
   if (scheme.EqualsLiteral("resource")) {
@@ -739,6 +779,7 @@ nsLayoutStylesheetCache::LoadSheet(nsIURI* aURI,
   }
 
 
+  nsZipArchive::sFileCorruptedReason = nullptr;
   nsresult rv = gCSSLoader->LoadSheetSync(aURI, aParsingMode, true,
                                           getter_AddRefs(aSheet));
   if (NS_FAILED(rv)) {
diff --git a/modules/libjar/nsJAR.cpp b/modules/libjar/nsJAR.cpp
index 8ea93e7a5d6..b50289124a3 100644
--- a/modules/libjar/nsJAR.cpp
+++ b/modules/libjar/nsJAR.cpp
@@ -446,14 +446,19 @@ nsJAR::LoadEntry(const nsACString &aFilename, char** aBuf, uint32_t* aBufLen)
   uint64_t len64;
   rv = manifestStream->Available(&len64);
   if (NS_FAILED(rv)) return rv;
-  NS_ENSURE_TRUE(len64 < UINT32_MAX, NS_ERROR_FILE_CORRUPTED); // bug 164695
+  if (len64 >= UINT32_MAX) { // bug 164695
+    nsZipArchive::sFileCorruptedReason = "nsJAR: invalid manifest size";
+    return NS_ERROR_FILE_CORRUPTED;
+  }
   uint32_t len = (uint32_t)len64;
   buf = (char*)malloc(len+1);
   if (!buf) return NS_ERROR_OUT_OF_MEMORY;
   uint32_t bytesRead;
   rv = manifestStream->Read(buf, len, &bytesRead);
-  if (bytesRead != len)
+  if (bytesRead != len) {
+    nsZipArchive::sFileCorruptedReason = "nsJAR: manifest too small";
     rv = NS_ERROR_FILE_CORRUPTED;
+  }
   if (NS_FAILED(rv)) {
     free(buf);
     return rv;
@@ -539,6 +544,7 @@ nsJAR::ParseManifest()
   if (more)
   {
     mParsedManifest = true;
+    nsZipArchive::sFileCorruptedReason = "nsJAR: duplicate manifests";
     return NS_ERROR_FILE_CORRUPTED; // More than one MF file
   }
 
@@ -638,8 +644,10 @@ nsJAR::ParseOneFile(const char* filebuf, int16_t aFileType)
   curLine.Assign(filebuf, linelen);
 
   if ( ((aFileType == JAR_MF) && !curLine.Equals(JAR_MF_HEADER) ) ||
-       ((aFileType == JAR_SF) && !curLine.Equals(JAR_SF_HEADER) ) )
+       ((aFileType == JAR_SF) && !curLine.Equals(JAR_SF_HEADER) ) ) {
+     nsZipArchive::sFileCorruptedReason = "nsJAR: invalid manifest header";
      return NS_ERROR_FILE_CORRUPTED;
+  }
 
   //-- Skip header section
   do {
diff --git a/modules/libjar/nsJARInputStream.cpp b/modules/libjar/nsJARInputStream.cpp
index 4a4c1d64cf3..4df5d7a0495 100644
--- a/modules/libjar/nsJARInputStream.cpp
+++ b/modules/libjar/nsJARInputStream.cpp
@@ -58,8 +58,10 @@ nsJARInputStream::InitFile(nsJAR *aJar, nsZipItem *item)
     // Must keep handle to filepointer and mmap structure as long as we need access to the mmapped data
     mFd = aJar->mZip->GetFD();
     mZs.next_in = (Bytef *)aJar->mZip->GetData(item);
-    if (!mZs.next_in)
+    if (!mZs.next_in) {
+        nsZipArchive::sFileCorruptedReason = "nsJARInputStream: !mZs.next_in";
         return NS_ERROR_FILE_CORRUPTED;
+    }
     mZs.avail_in = item->Size();
     mOutSize = item->RealSize();
     mZs.total_out = 0;
@@ -266,8 +268,10 @@ nsJARInputStream::ContinueInflate(char* aBuffer, uint32_t aCount,
 
     // now inflate
     int zerr = inflate(&mZs, Z_SYNC_FLUSH);
-    if ((zerr != Z_OK) && (zerr != Z_STREAM_END))
+    if ((zerr != Z_OK) && (zerr != Z_STREAM_END)) {
+        nsZipArchive::sFileCorruptedReason = "nsJARInputStream: error while inflating";
         return NS_ERROR_FILE_CORRUPTED;
+    }
 
     *aBytesRead = (mZs.total_out - oldTotalOut);
 
@@ -280,8 +284,10 @@ nsJARInputStream::ContinueInflate(char* aBuffer, uint32_t aCount,
         inflateEnd(&mZs);
 
         // stop returning valid data as soon as we know we have a bad CRC
-        if (mOutCrc != mInCrc)
+        if (mOutCrc != mInCrc) {
+            nsZipArchive::sFileCorruptedReason = "nsJARInputStream: crc mismatch";
             return NS_ERROR_FILE_CORRUPTED;
+        }
     }
 
     return NS_OK;
diff --git a/modules/libjar/nsZipArchive.cpp b/modules/libjar/nsZipArchive.cpp
index 508319b5e75..568d0b68eab 100644
--- a/modules/libjar/nsZipArchive.cpp
+++ b/modules/libjar/nsZipArchive.cpp
@@ -444,6 +444,7 @@ nsresult nsZipArchive::ExtractFile(nsZipItem *item, const char *outname,
     uint32_t count = 0;
     uint8_t* buf = cursor.Read(&count);
     if (!buf) {
+      nsZipArchive::sFileCorruptedReason = "nsZipArchive: Read() failed to return a buffer";
       rv = NS_ERROR_FILE_CORRUPTED;
       break;
     } else if (count == 0) {
@@ -644,22 +645,28 @@ MOZ_WIN_MEM_TRY_BEGIN
       }
   }
 
-  if (!centralOffset)
+  if (!centralOffset) {
+    nsZipArchive::sFileCorruptedReason = "nsZipArchive: no central offset";
     return NS_ERROR_FILE_CORRUPTED;
+  }
 
   buf = startp + centralOffset;
 
   // avoid overflow of startp + centralOffset.
-  if (buf < startp)
+  if (buf < startp) {
+    nsZipArchive::sFileCorruptedReason = "nsZipArchive: overflow looking for central directory";
     return NS_ERROR_FILE_CORRUPTED;
+  }
 
   //-- Read the central directory headers
   uint32_t sig = 0;
   while (buf + int32_t(sizeof(uint32_t)) <= endp &&
          (sig = xtolong(buf)) == CENTRALSIG) {
     // Make sure there is enough data available.
-    if (endp - buf < ZIPCENTRAL_SIZE)
+    if (endp - buf < ZIPCENTRAL_SIZE) {
+      nsZipArchive::sFileCorruptedReason = "nsZipArchive: central directory too small";
       return NS_ERROR_FILE_CORRUPTED;
+    }
 
     // Read the fixed-size data.
     ZipCentral* central = (ZipCentral*)buf;
@@ -672,9 +679,13 @@ MOZ_WIN_MEM_TRY_BEGIN
     // Sanity check variable sizes and refuse to deal with
     // anything too big: it's likely a corrupt archive.
     if (namelen < 1 ||
-        namelen > kMaxNameLength ||
-        buf >= buf + diff || // No overflow
+        namelen > kMaxNameLength) {
+      nsZipArchive::sFileCorruptedReason = "nsZipArchive: namelen out of range";
+      return NS_ERROR_FILE_CORRUPTED;
+    }
+    if (buf >= buf + diff || // No overflow
         buf >= endp - diff) {
+      nsZipArchive::sFileCorruptedReason = "nsZipArchive: overflow looking for next item";
       return NS_ERROR_FILE_CORRUPTED;
     }
 
@@ -697,8 +708,10 @@ MOZ_WIN_MEM_TRY_BEGIN
     sig = 0;
   } /* while reading central directory records */
 
-  if (sig != ENDSIG)
+  if (sig != ENDSIG) {
+    nsZipArchive::sFileCorruptedReason = "nsZipArchive: unexpected sig";
     return NS_ERROR_FILE_CORRUPTED;
+  }
 
   // Make the comment available for consumers.
   if (endp - buf >= ZIPEND_SIZE) {
@@ -1213,3 +1226,6 @@ nsZipItemPtr_base::nsZipItemPtr_base(nsZipArchive *aZip,
     return;
   }
 }
+
+/* static */ const char*
+nsZipArchive::sFileCorruptedReason = nullptr;
diff --git a/modules/libjar/nsZipArchive.h b/modules/libjar/nsZipArchive.h
index 242ee4a3c8b..73a524e9918 100644
--- a/modules/libjar/nsZipArchive.h
+++ b/modules/libjar/nsZipArchive.h
@@ -102,6 +102,8 @@ class nsZipArchive final
   ~nsZipArchive();
 
 public:
+  static const char* sFileCorruptedReason;
+
   /** constructing does not open the archive. See OpenArchive() */
   nsZipArchive();
 
diff --git a/xpcom/build/FileLocation.cpp b/xpcom/build/FileLocation.cpp
index 67a558b4b10..73ea5c57852 100644
--- a/xpcom/build/FileLocation.cpp
+++ b/xpcom/build/FileLocation.cpp
@@ -233,7 +233,11 @@ FileLocation::Data::Copy(char* aBuf, uint32_t aLen)
                        aLen, true);
     uint32_t readLen;
     cursor.Copy(&readLen);
-    return (readLen == aLen) ? NS_OK : NS_ERROR_FILE_CORRUPTED;
+    if (readLen != aLen) {
+      nsZipArchive::sFileCorruptedReason = "FileLocation::Data: insufficient data";
+      return NS_ERROR_FILE_CORRUPTED;
+    }
+    return NS_OK;
   }
 #endif // !defined(MOZILLA_XPCOMRT_API)
   return NS_ERROR_NOT_INITIALIZED;