fixes #10744: back to solid borders on carets

dist/css/bootstrap.css

@@ -3462,7 +3462,6 @@ input[type="button"].btn-block {
   vertical-align: middle;
   border-top: 4px solid #000000;
   border-right: 4px solid transparent;
-  border-bottom: 0 dotted;
   border-left: 4px solid transparent;
 }
 
@@ -3580,7 +3579,7 @@ input[type="button"].btn-block {
 
 .dropup .caret,
 .navbar-fixed-bottom .dropdown .caret {
-  border-top: 0 dotted;
+  border-top: 0;
   border-bottom: 4px solid #000000;
   content: "";
 }

less/dropdowns.less

@@ -13,9 +13,6 @@
   border-top:   @caret-width-base solid @dropdown-caret-color;
   border-right: @caret-width-base solid transparent;
   border-left:  @caret-width-base solid transparent;
-  // Firefox fix for https://github.com/twbs/bootstrap/issues/9538. Once fixed,
-  // we can just straight up remove this.
-  border-bottom: 0 dotted;
 }
 
 // The dropdown wrapper (div)
@@ -163,9 +160,7 @@
 .navbar-fixed-bottom .dropdown {
   // Reverse the caret
   .caret {
-    // Firefox fix for https://github.com/twbs/bootstrap/issues/9538. Once this
-    // gets fixed, restore `border-top: 0;`.
-    border-top: 0 dotted;
+    border-top: 0;
     border-bottom: @caret-width-base solid @dropdown-caret-color;
     content: "";
   }