Yep, detecting opera.

Goal can be achieved with two different svg styles,
but Opera only implements one, Firefox the other. Can't
apply both because Chrome implements both.

css/map.css

@@ -648,7 +648,13 @@ text.pointlabel {
 }
 
 .pathlabel .textpath {
+  dominant-baseline: middle;
+}
+
+/* Opera doesn't support dominant-baseline */
+.opera .pathlabel .textpath {
   baseline-shift: -33%;
+  dominant-baseline: auto;
 }
 
 .pointlabel-halo,

js/id/id.js

@@ -127,6 +127,8 @@ iD.detect = function() {
         browser.support = true;
     }
 
+    browser.opera = ua.indexOf('Opera') >= 0;
+
     browser.locale = navigator.language;
 
     function nav(x) {

js/id/ui.js

@@ -12,6 +12,8 @@ iD.ui = function(context) {
             return;
         }
 
+        if (iD.detect().opera) container.classed('opera', true);
+
         function hintprefix(x, y) {
             return '<span>' + y + '</span>' + '<div class="keyhint-wrap"><span class="keyhint"> ' + x + '</span></div>';
         }