Bug 1700871 - Only allow focus move for links / form submission iff actually handling user input. r=smaug

The other navigation that allows focus moves (window.open) already goes
through the popup blocker, so that one is fine.

I think given how weird yet conservative other browsers are, this should
be a good trade-off to avoid false positives.

Differential Revision: https://phabricator.services.mozilla.com/D110196

dom/html/HTMLFormElement.cpp

@@ -825,6 +825,7 @@ nsresult HTMLFormElement::SubmitSubmission(
     loadState->SetTriggeringPrincipal(NodePrincipal());
     loadState->SetPrincipalToInherit(NodePrincipal());
     loadState->SetCsp(GetCsp());
+    loadState->SetAllowFocusMove(UserActivation::IsHandlingUserInput());
 
     rv = nsDocShell::Cast(container)->OnLinkClickSync(this, loadState, false,
                                                       NodePrincipal());