Fix Bug 1515663 - Block FxA snippet on form submit (#4635)

content-src/asrouter/templates/SubmitFormSnippet/SubmitFormSnippet.jsx

@@ -38,6 +38,7 @@ export class SubmitFormSnippet extends React.PureComponent {
     this.props.sendUserActionTelemetry({event: "CLICK_BUTTON", value: "conversion-subscribe-activation", id: "NEWTAB_FOOTER_BAR_CONTENT"});
 
     if (this.props.form_method.toUpperCase() === "GET") {
+      this.props.onBlock({preventDismiss: true});
       this.refs.form.submit();
       return;
     }

test/unit/asrouter/templates/SubmitFormSnippet.test.jsx

@@ -249,5 +249,14 @@ describe("SubmitFormSnippet", () => {
 
       assert.notCalled(window.fetch);
     });
+    it("should block the snippet when form_method is GET", () => {
+      wrapper.setProps({form_method: "GET"});
+      wrapper.setState({expanded: true});
+
+      wrapper.instance().handleSubmit({preventDefault: sandbox.stub()});
+
+      assert.calledOnce(onBlockStub);
+      assert.calledWithExactly(onBlockStub, {preventDismiss: true});
+    });
   });
 });