--- a/dom/media/FileBlockCache.cpp
+++ b/dom/media/FileBlockCache.cpp
@@ -18,17 +18,16 @@ namespace mozilla {
 #undef LOG
 LazyLogModule gFileBlockCacheLog("FileBlockCache");
 #define LOG(x, ...) MOZ_LOG(gFileBlockCacheLog, LogLevel::Debug, \
   ("%p " x, this, ##__VA_ARGS__))
 
 void
 FileBlockCache::SetCacheFile(PRFileDesc* aFD)
 {
-  MOZ_ASSERT(NS_IsMainThread());
   LOG("SetFD(aFD=%p) mIsOpen=%d", aFD, mIsOpen);
 
   if (!aFD) {
     // Failed to get a temporary file. Shutdown.
     Close();
     return;
   }
   {
@@ -51,18 +50,16 @@ FileBlockCache::SetCacheFile(PRFileDesc*
   }
 }
 
 nsresult
 FileBlockCache::Init()
 {
   LOG("Init()");
 
-  MOZ_ASSERT(NS_IsMainThread());
-
   MonitorAutoLock mon(mDataMonitor);
   nsresult rv = NS_NewNamedThread("FileBlockCache",
                                   getter_AddRefs(mThread),
                                   nullptr,
                                   SharedThreadPool::kStackSize);
   if (NS_FAILED(rv)) {
     return rv;
   }
@@ -114,18 +111,16 @@ FileBlockCache::~FileBlockCache()
     }
   }
 }
 
 void FileBlockCache::Close()
 {
   LOG("Close()");
 
-  NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
-
   MonitorAutoLock mon(mDataMonitor);
   if (!mIsOpen) {
     return;
   }
   mIsOpen = false;
   if (!mThread) {
     return;
   }
@@ -383,17 +378,16 @@ nsresult FileBlockCache::Read(int64_t aO
     bytesToRead -= bytesRead;
   }
   *aBytes = aLength - bytesToRead;
   return NS_OK;
 }
 
 nsresult FileBlockCache::MoveBlock(int32_t aSourceBlockIndex, int32_t aDestBlockIndex)
 {
-  NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
   MonitorAutoLock mon(mDataMonitor);
 
   if (!mIsOpen)
     return NS_ERROR_FAILURE;
 
   mBlockChanges.EnsureLengthAtLeast(std::max(aSourceBlockIndex, aDestBlockIndex) + 1);
 
   // The source block's contents may be the destination of another pending