Fix intermittent test (#5736)

Author: jasonLaster

src/test/mochitest/browser_dbg-editor-select.js

@@ -21,13 +21,13 @@ add_task(async function() {
   // Call the function that we set a breakpoint in.
   invokeInTab("main");
   await waitForPaused(dbg);
-  await waitForLoadedSource(dbg, "simple1");
+  await waitForSelectedSource(dbg, "simple1");
   assertPausedLocation(dbg);
 
   // Step through to another file and make sure it's paused in the
   // right place.
   await stepIn(dbg);
-  await waitForLoadedSource(dbg, "simple2");
+  await waitForSelectedSource(dbg, "simple2");
   assertPausedLocation(dbg);
 
   // Step back out to the initial file.
@@ -43,7 +43,7 @@ add_task(async function() {
 
   invokeInTab("testModel");
   await waitForPaused(dbg);
-  await waitForLoadedSource(dbg, "long.js");
+  await waitForSelectedSource(dbg, "long.js");
 
   assertPausedLocation(dbg);
   ok(