As a diehard IEOnly, I have never used Firefox seriously. From the perspective of a hypocritical Web programmer, it is a failure. After digging, I found that the plug-ins under Firefox are really full of tricks.

No, there is such a little thing: Firebug, fireflies. What an interesting little thing. You can use this extension to directly edit, debug, and monitor CSS, HTML, and JavaScript.

Firebug currently has the following features:

it includes a step-by-step JavaScript debugger.
Use the status bar icon to monitor errors in your web page.
Errors from JavaScript and CSS can be displayed in the console.
Messages from JavaScript can be recorded.
Contains the JavaScript command line.
You can monitor XMLHttpRequest traffic.
You can check the HTML source code, measure styles, events, layout, and DOM.

You have been using EditPlus to write JavaScript for some time, which has become a big problem for debugging. This time, it seems that you can throw away the damn alert() method.

There's an interesting saying on Firebug:

Web developers have suffered with "alert debugging" for centuries. If you enjoy clicking the "Ok" button 40,000 times a day, FireBug is not for you. Otherwise, you'll enjoy having the ability to log messages from JavaScript in your web page directly to the FireBug console.

To put it bluntly:

Web programmers have endured "alert debugging" for centuries. If you're happy to click the "OK" button 40,000 times a day, FireBug is not for you. Otherwise, you will happily have the ability to log JavaScript information from your web pages to FireBug's console.

Firebug from: www.getfirebug.com for Firefox 1.5 - 2.0.0.* version