When you use the Firefox browser as much as me, and you are developing with Javascript, there’s no need to use the dirty pop-up box, the Javascript alert anymore. Simple log to your Firebug console.

The Firebug extension is needed: Download Firebug.
(Make sure you have enabled the console in Firebug, and checked Chrome Messages in Options menu.)

var msg = "See me logging this in Firebug!";
console.log(msg);

It’s also possible to show error or warning logs in Firebug:

console.error("This is an error message");
console.warn("Note: this is a warning!");

You can use Firebug also for converting characters with url encoding:
Just type in the Firebug console, see the example with the ‘@’ sign:

escape("@");