Bug 1762889 - Add parsingIndex after running fathom heuristics for a field r=tgiles

Differential Revision: https://phabricator.services.mozilla.com/D142824

toolkit/components/formautofill/FormAutofillHeuristics.jsm

@@ -880,6 +880,7 @@ this.FormAutofillHeuristics = {
     // The heuristic below should be covered by fathom rules, so we can skip doing
     // it.
     if (FormAutofillUtils.isFathomCreditCardsEnabled()) {
+      fieldScanner.parsingIndex++;
       return true;
     }