Bug 1532397 - Fix multiple highlight issues in debugger r=jlast

https://github.com/firefox-devtools/debugger/issues/7954

Differential Revision: https://phabricator.services.mozilla.com/D21989

--HG--
extra : moz-landing-system : lando

devtools/client/debugger/new/src/components/Editor/Preview/index.js

@@ -50,10 +50,14 @@ function inPopup(e) {
 
 function getElementFromPos(pos: DOMRect) {
   // $FlowIgnore
-  return document.elementFromPoint(
+  // We need to use element*s*AtPoint because the tooltip overlays
+  // the token and thus an undesirable element may be returned
+  const elementsAtPoint = [...document.elementsFromPoint(
     pos.x + pos.width / 2,
     pos.y + pos.height / 2
-  );
+  )];
+
+  return elementsAtPoint.find(el => el.className.startsWith("cm-"));
 }
 
 class Preview extends PureComponent<Props, State> {