Removed the transformation for file input al together. Should test of this works correctly for IE and Opera.

less/fileinput.less

@@ -13,8 +13,6 @@
     margin: 0;
     opacity: 0;
     filter: alpha(opacity=0);
-    transform: translate(-300px, 0) scale(4);
-    -webkit-transform: translate(-300px, 0) scale(4);
     font-size: 23px;
     height: 100%;
     width: 100%;
@@ -23,12 +21,6 @@
   }
 }
 
-@-moz-document url-prefix() {
-  .btn-file > input {
-    transform: none;
-  }
-}
-
 .fileinput {
   margin-bottom: 9px;
   display: inline-block;