Ditch `&`, as `+ ...` is enought

less/breadcrumbs.less

@@ -11,7 +11,7 @@
   border-radius: @border-radius-base;
   > li {
     display: inline-block;
-    &+li:before {
+    + li:before {
       content: "@{breadcrumb-separator}\00a0"; // Unicode space added since inline-block means non-collapsing white-space
       padding: 0 5px;
       color: @breadcrumb-color;