fix #10252 by restricting Android Firefox reset to only .form-control & .btn

dist/css/bootstrap.css

@@ -316,13 +316,6 @@ textarea {
   line-height: inherit;
 }
 
-button,
-input,
-select[multiple],
-textarea {
-  background-image: none;
-}
-
 a {
   color: #428bca;
   text-decoration: none;
@@ -1724,6 +1717,7 @@ output {
   color: #555555;
   vertical-align: middle;
   background-color: #ffffff;
+  background-image: none;
   border: 1px solid #cccccc;
   border-radius: 4px;
   -webkit-box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.075);
@@ -2006,6 +2000,7 @@ textarea.input-lg {
   white-space: nowrap;
   vertical-align: middle;
   cursor: pointer;
+  background-image: none;
   border: 1px solid transparent;
   border-radius: 4px;
   -webkit-user-select: none;

less/buttons.less

@@ -17,6 +17,7 @@
   text-align: center;
   vertical-align: middle;
   cursor: pointer;
+  background-image: none; // Reset unusual Firefox-on-Android default style; see https://github.com/necolas/normalize.css/issues/214
   border: 1px solid transparent;
   border-radius: @border-radius-base;
   white-space: nowrap;

less/forms.less

@@ -133,6 +133,7 @@ output {
   color: @input-color;
   vertical-align: middle;
   background-color: @input-bg;
+  background-image: none; // Reset unusual Firefox-on-Android default style; see https://github.com/necolas/normalize.css/issues/214
   border: 1px solid @input-border;
   border-radius: @input-border-radius;
   .box-shadow(inset 0 1px 1px rgba(0,0,0,.075));

less/scaffolding.less

@@ -37,17 +37,6 @@ textarea {
   line-height: inherit;
 }
 
-// Reset unusual Firefox-on-Android default style.
-//
-// See https://github.com/necolas/normalize.css/issues/214
-
-button,
-input,
-select[multiple],
-textarea {
-  background-image: none;
-}
-
 
 // Links