--- a/python/mozbuild/mozpack/files.py
+++ b/python/mozbuild/mozpack/files.py
@@ -500,16 +500,21 @@ class DeflatedFile(BaseFile):
         from mozpack.mozjar import JarFileReader
         assert isinstance(file, JarFileReader)
         self.file = file
 
     def open(self):
         self.file.seek(0)
         return self.file
 
+    def read(self):
+        '''Return the contents of the file.'''
+        self.file.seek(0)
+        return self.file.read()
+
 
 class XPTFile(GeneratedFile):
     '''
     File class for a linked XPT file. It takes several XPT files as input
     (using the add() and remove() member functions), and links them at copy()
     time.
     '''
     def __init__(self):