Index: docs/ClangFormatStyleOptions.rst
===================================================================
--- docs/ClangFormatStyleOptions.rst
+++ docs/ClangFormatStyleOptions.rst
@@ -275,6 +275,9 @@
   * ``BS_Linux`` (in configuration: ``Linux``)
     Like ``Attach``, but break before braces on function, namespace and
     class definitions.
+  * ``BS_Mozilla`` (in configuration: ``Mozilla``)
+    Like ``Attach``, but break before braces on function and record
+    definitions.
   * ``BS_Stroustrup`` (in configuration: ``Stroustrup``)
     Like ``Attach``, but break before function definitions, and 'else'.
   * ``BS_Allman`` (in configuration: ``Allman``)
Index: include/clang/Format/Format.h
===================================================================
--- include/clang/Format/Format.h
+++ include/clang/Format/Format.h
@@ -166,6 +166,9 @@
     /// Like \c Attach, but break before braces on function, namespace and
     /// class definitions.
     BS_Linux,
+    /// Like \c Attach, but break before braces on function and record
+    /// definitions.
+    BS_Mozilla,
     /// Like \c Attach, but break before function definitions, and 'else'.
     BS_Stroustrup,
     /// Always break before braces.
Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp
+++ lib/Format/Format.cpp
@@ -93,6 +93,7 @@
   static void enumeration(IO &IO, FormatStyle::BraceBreakingStyle &Value) {
     IO.enumCase(Value, "Attach", FormatStyle::BS_Attach);
     IO.enumCase(Value, "Linux", FormatStyle::BS_Linux);
+    IO.enumCase(Value, "Mozilla", FormatStyle::BS_Mozilla);
     IO.enumCase(Value, "Stroustrup", FormatStyle::BS_Stroustrup);
     IO.enumCase(Value, "Allman", FormatStyle::BS_Allman);
     IO.enumCase(Value, "GNU", FormatStyle::BS_GNU);
@@ -478,6 +479,7 @@
   MozillaStyle.AlwaysBreakAfterDefinitionReturnType =
       FormatStyle::DRTBS_TopLevel;
   MozillaStyle.AlwaysBreakTemplateDeclarations = true;
+  MozillaStyle.BreakBeforeBraces = FormatStyle::BS_Mozilla;
   MozillaStyle.BreakConstructorInitializersBeforeComma = true;
   MozillaStyle.ConstructorInitializerIndentWidth = 2;
   MozillaStyle.ContinuationIndentWidth = 2;
Index: lib/Format/UnwrappedLineParser.cpp
===================================================================
--- lib/Format/UnwrappedLineParser.cpp
+++ lib/Format/UnwrappedLineParser.cpp
@@ -439,6 +439,9 @@
   switch (Style.BreakBeforeBraces) {
   case FormatStyle::BS_Linux:
     return InitialToken.isOneOf(tok::kw_namespace, tok::kw_class);
+  case FormatStyle::BS_Mozilla:
+    return InitialToken.isOneOf(tok::kw_class, tok::kw_enum, tok::kw_struct,
+                                tok::kw_union);
   case FormatStyle::BS_Allman:
   case FormatStyle::BS_GNU:
     return true;
@@ -1491,6 +1494,8 @@
 }
 
 void UnwrappedLineParser::parseEnum() {
+  const FormatToken &InitialToken = *FormatTok;
+
   // Won't be 'enum' for NS_ENUMs.
   if (FormatTok->Tok.is(tok::kw_enum))
     nextToken();
@@ -1519,6 +1524,11 @@
   // Just a declaration or something is wrong.
   if (FormatTok->isNot(tok::l_brace))
     return;
+
+  const bool BreakBeforeBrace = ShouldBreakBeforeBrace(Style, InitialToken);
+  if (BreakBeforeBrace)
+    addUnwrappedLine();
+
   FormatTok->BlockKind = BK_Block;
 
   if (Style.Language == FormatStyle::LK_Java) {
@@ -1527,6 +1537,12 @@
     return;
   }
 
+  if (BreakBeforeBrace) {
+    parseBlock(/*MustBeDeclaration=*/false, /*AddLevel=*/true,
+               /*MunchSemi=*/false);
+    return;
+  }
+
   // Parse enum body.
   bool HasError = !parseBracedList(/*ContinueOnSemicolons=*/true);
   if (HasError) {
Index: unittests/Format/FormatTest.cpp
===================================================================
--- unittests/Format/FormatTest.cpp
+++ unittests/Format/FormatTest.cpp
@@ -8547,6 +8547,47 @@
                LinuxBraceStyle);
 }
 
+TEST_F(FormatTest, MozillaBraceBreaking) {
+  FormatStyle MozillaBraceStyle = getLLVMStyle();
+  MozillaBraceStyle.BreakBeforeBraces = FormatStyle::BS_Mozilla;
+  verifyFormat("namespace a {\n"
+               "class A\n"
+               "{\n"
+               "  void f()\n"
+               "  {\n"
+               "    if (true) {\n"
+               "      a();\n"
+               "      b();\n"
+               "    }\n"
+               "  }\n"
+               "  void g() { return; }\n"
+               "};\n"
+               "enum E\n"
+               "{\n"
+               "  FOO;\n"
+               "};\n"
+               "struct B\n"
+               "{\n"
+               "  int x;\n"
+               "};\n"
+               "}\n",
+               MozillaBraceStyle);
+  verifyFormat("struct S\n"
+               "{\n"
+               "  int Type;\n"
+               "  union\n"
+               "  {\n"
+               "    int x;\n"
+               "    double y;\n"
+               "  } Value;\n"
+               "  class C\n"
+               "  {\n"
+               "    MyFavoriteType Value;\n"
+               "  } Class;\n"
+               "}\n",
+               MozillaBraceStyle);
+}
+
 TEST_F(FormatTest, StroustrupBraceBreaking) {
   FormatStyle StroustrupBraceStyle = getLLVMStyle();
   StroustrupBraceStyle.BreakBeforeBraces = FormatStyle::BS_Stroustrup;
@@ -9187,6 +9228,8 @@
               FormatStyle::BS_Attach);
   CHECK_PARSE("BreakBeforeBraces: Linux", BreakBeforeBraces,
               FormatStyle::BS_Linux);
+  CHECK_PARSE("BreakBeforeBraces: Mozilla", BreakBeforeBraces,
+              FormatStyle::BS_Mozilla);
   CHECK_PARSE("BreakBeforeBraces: Stroustrup", BreakBeforeBraces,
               FormatStyle::BS_Stroustrup);
   CHECK_PARSE("BreakBeforeBraces: Allman", BreakBeforeBraces,