Tag Archives: alert

Overriding Firefox’s Window.Alert – Part 1

Window.alert is a native function built into Firefox – but that doesn’t mean it can’t be overridden.

Check this out:

Open Firebug, and get to the console.  Then, click that little red arrow at the end of the input line so that you get the large box input on the right side of the screen.

Type this into the input box:

var alert_count = 0;
var old_alert = window.alert;
var alert_max = 5;
window.alert = function(alert_text) {
  if (alert_count < alert_max) {
    ++alert_count;
    old_alert(alert_text);
  } else {
    console.log("Reached maximum alerts");
  }
}

Now, hit “Run” at the bottom of that input window.  We’ve just overridden the window.alert function during runtime.

Hit “Clear” at the bottom of the input window, and type in:

for (i = 0; i < 10; ++i) {
  alert(i);
}

Hit “Run”.  Click “OK” for the first 5 alert windows, and watch as the rest of them are spewed out to the console.  Nice.

So, I don’t think this helps me much in creating my plug-in, but it’s interesting to see how window.alert is malliable at run-time.

This seems to be a more relevant discovery – Mozilla’s Chrome lets me create an alert popup with a checkbox using alertCheck.  I think this is exactly what I’m looking for.

I’ll tinker with it over the next few days, and post some code.

Summer Project: Firefox Plugin to Override Window.Alert

When I don’t have work to do, I get antsy.

And right now, I’ve got no work to do.

So I’ve come up with a project for myself:  remember how I created a Firefox Plugin a few months back?  I’d like to make another one – but this one will actually serve a useful purpose.

Have you ever been to a page that suddenly started spewing window.alert boxes at you?

If you haven’t, open up Firebug, and paste this into the console:

for(i = 0; i < 10; ++i){ alert(i); }

Now imagine if instead of 10 alert boxes, it spewed hundreds…or thousands….or god forbid, it uses a while(true) loop, and throws infinity alert boxes at you.

It totally cripples Firefox. It’s a super simple browser DoS attack.

Mozilla knows this, but so far, no solution except for killing the Firefox process, or disabling Javascript manually, or with NoScript (a plugin that I highly recommend).

Google Chrome has solved this problem by providing a checkbox on alert dialogs that allow a user to disable future popups from the current site.

Cool.  I want Firefox to have the same feature.

So, this summer, I’m going to try to build a Firefox Plugin that will override the standard window.alert function, with one that provides a checkbox, letting the user disable future alerts.

I don’t even know if this is possible, but I’m looking into it.

I’ll blog my research and progress as I go along, and share my code / final plugin when it’s all finished (or when I abandon it…hey, it happens).

So stay tuned.