diff --git a/static/bootstrap/stylesheets/bootstrap/mixins/_tab-focus.scss b/static/bootstrap/stylesheets/bootstrap/mixins/_tab-focus.scss
new file mode 100644
index 0000000000000000000000000000000000000000..f16ed6428aac35b4bc86d9c18501f651632d2adf
--- /dev/null
+++ b/static/bootstrap/stylesheets/bootstrap/mixins/_tab-focus.scss
@@ -0,0 +1,9 @@
+// WebKit-style focus
+
+@mixin tab-focus() {
+  // WebKit-specific. Other browsers will keep their default outline style.
+  // (Initially tried to also force default via `outline: initial`,
+  // but that seems to erroneously remove the outline in Firefox altogether.)
+  outline: 5px auto -webkit-focus-ring-color;
+  outline-offset: -2px;
+}