Put the quirky 1em bottom margin on forms only in quirks mode. Bug 41806,

patch by Anne van Kesteren <bug@annevankesteren.nl>, r=bzbarsky, sr=dbaron

layout/style/forms.css

@@ -47,11 +47,6 @@
   height: 100%;   /* Need this so percentage heights of kids work right */
 }
 
-form {
-  display: block;
-  margin: 0 0 1em 0;
-}
-
 /* miscellaneous form elements */
 
 legend {

layout/style/html.css

@@ -53,7 +53,7 @@ bdo[dir] {
 
 /* blocks */
 
-html, div, map, dt, isindex {
+html, div, map, dt, isindex, form {
   display: block;
 }
 

layout/style/quirk.css

@@ -275,3 +275,8 @@ img[align=right] {
 input:not([type=image]), textarea {
   -moz-box-sizing: border-box;
 }
+
+/* Quirk: give form margin for compat (b=41806) */
+form{
+ margin: 0 0 1em 0;
+}