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Whether you’re a front-end graphics designer or a back-end web programmer, if you’ve worked long enough in the field of creating web-based solutions, you’ve no doubt heard about an extension for the Mozilla Firefox web browser called (simply enough) the Web Developer extension. If you have no clue what I’m talking about, here’s a brief overview from Webs Tips to get you familiarized with this wonderful tool.

This article lists some practical, everyday uses of the Web Developer extension to help improve your web-building methods. I’ve tried to stay away from the more common and basic uses of the Web Developer extension like troubleshooting layout issues with the Information > Display Div Order option because I feel these have been discussed quite enough in other places. New users, don’t run away quite yet, I think this guide will help you get a rapid jump start into applying this tool into your daily development routine.

So without further ado, here’s nine highly pragmatic uses of the Web Developer extension for Firefox.

1) Change XHTML on-the-fly without changing your web files.

Unfortunately for many developers, we don’t all have the luxury of testing servers and sandbox environments. I for one, confess to developing on live websites even during peak web traffic times.

If you’d like to lessen customer support requests due to an inadvertent display:none; property assignment on the log-in box — use the Web Developer extension to effortlessly check your XHTML modifications before you commit them to the server.

Here’s an (extreme) example of how I was able to change a few of reddit’s XHTML marku

And here’s the modified version:

As you can see in the above picture, I changed the top three stories (to something else I’d much read about) and modified the background color to pink (I have an odd affection towards hot pink for some reason).

You can achieve the same results by using the Miscellaneous > Edit HTML Markup option which will open up the Edit HTML tab panel displaying the XHTML of the web page. Unfortunately, the window isn’t color-coded and the Search HTML function doesn’t quite work properly (yet).

Tip: You can change the position of the Edit HTML panel by clicking on the Position icon (right next to the Edit HTML tab on the above screenshot).

To change the CSS styles of the page, use the CSS > Edit CSS option, which will allow you to edit the styles used on the web page.

2) Measure things quickly with the Ruler Tool.

Raise your hand if you’ve ever print-screen’ed, and then copy-&-paste’d the screenshot onto Photoshop just to determine dimensions of certain page objects (like the width of an image) with the selection tool. *Raises hand in shame*

With the Ruler Tool (enable it via Miscellaneous > Display Ruler Tool), you can speedily size-up objects inside the web browser. It’s a great tool in conjunction with outline options such as Information > Display Div Order option or Information > Display Block Size option, allowing you to detect the amount of padding and margin between elements.

3) See how web pages look on a non-traditional web browser.

Nowadays, tons of people have mobile devices that lets them view web pages in non-traditional ways. Determine whether your pages render correctly (or close enough) on portable device screens by using the Miscellaneous > Small Screen Rendering option. This saves you from going out and purchasing a Blackberry or a Trio with an internet dataplan just for cross-browser checking.

What it will look like on a Small Screen Rendering device…

4) Find out how optimized your page is.

Use the Tools > View Speed Report option to automatically send your page to WebSiteOptimization.com, a site that provides a plethora of information about your web page load times like how quickly your page loads and how many HTTP connections are being used among a ton of other things.

There are built-in tools in Adobe Dreamweaver and Flash (if you even have access to them) that simulates download speeds, but nothing beats a free, comprehensive and actual live speed report.

5) Populate web form fields instantly.

Don’t you hate it when you have to fill in your custom-built web form for the nth time because you’re testing it? You can quit tabbing and entering junk information on your form fields and switch to using the Form > Populate Form Fields option in the Web Developer extension.

In the example below, you can see that it populates most web forms somewhat intelligently – It was able to guess the email field — but missed the phone number field.

6) Find all the CSS styles that affect an element.

For most fairly-proficient CSS developers, it’s quite easy to find the exact selectors that style an element’s properties – fyi: #selector { property: value; }. This is especially true when you’re the original author and/or the styles are contained in one stylesheet.

But what if you were working on someone else’s project… and the project in question has 1,000+ lines of pure CSS goodness, split into several external stylesheets (because Bob a.k.a. “Mr. Modularity” likes to keep things “simple“)? Another scenario you might encounter is being tasked to theme a content management system like Drupal or WordPress and you’re not quite sure where all the external stylesheets are.

For example, the Yahoo! home page has over 2,400 lines of CSS, spread over several external stylesheets and inline styles (Bob, you built this page didn’t you?).

If you’re tasked with revising this page, you have two choices: (1) look through, understand, and hunt down the styles you need or (2) decide that you’re smarter (and lazier) than that and so you use the CSS > View Style Information option of the Web Developer extension. With this option enabled, clicking on a page element opens up the Style Information panel which displays all the styles that affect the element.

7) View JavaScript and CSS source code in a jiffy.

One of the ways I troubleshoot rendering issues is by looking at how other web pages do it. JavaScript and CSS are often divided into several files — who wants to look through all of them?

Using the Information > View JavaScript and the CSS > View CSS options instantly displays all the JavaScript and CSS in a new browser tab. This has the side benefit of being able to aggregate all the CSS styles or JavaScript in one web page allowing you to use the Find tool of the Mozilla Firefox browser (keyboard shortcut: ctrl + f for PC users).

8) See how web pages are layered.

It’s often very helpful to determine which page div’s and objects are on a higher plane. Using the Information > View Topographic information gives you a visual representation of the depths of the page elements — darker shades are lower than lighter shades of gray.

9) See if your web page looks OK in different screen sizes.

I use a monitor size between 19 – 22 inches (wide screen). This can be problematic because many of our visitors use smaller monitors. Short of switching to a smaller LCD screen to simulate the user experience, I just use the Resize > Resize window option. It helps test whether my fluid layout works well in smaller windows (sometimes you forget to set min-widths for div elements and it jacks up the layout in smaller screen sizes), or if your fixed-width layout displays important content without user’s having to scroll.

Be sure to enable the Resize > Display Window Size in Title option to help you determine the exact dimensions, and also for documentation purposes when you’re taking screenshots of your webpages.

So there we are, nine ways you can employ the Mozilla Firefox Web Developer extension to better your web development experience. I don’t claim to be an expert, but I certainly know enough about the Web Developer extension to improve my web-building speed.