We all know by now that Firefox is a great tool, what most people don’t know is that Firefox works with the so called Extensions (small pieces of software that add features or small tweaks to you Firefox). Using Extensions is a blessing and they make your life on the internet a whole lot easier.

Here is a great collection of Firefox Extensions for webmasters:

1. Web Developer 1.1.4

This Extension adds a toolbar with some great features for easily editing the CSS, work on the accessibility of your site and other cool features. Get it here!

2. Firefox Accessibility Extension 1.01

Firefox Accessibility Extension makes it easier for people with a disability to view and navigate webpages, but it also helps developers to check the accessibility of their pages. Get it here!

3. SeoQuake 2.0.4

SeoQuake is huge, i use it every single day and it saves me a lot of time. This Extension basically adds a toolbar in the corner of the websites and with the push of a button it expands giving you almost instant information about the way search engines view and index that website, along with statistics from Alexa and other great features for the webmaster that works with Search Engine Optimisation. Also every time you search for something in Google, Yahoo or Msn you’ll get the same statistics under every result. Get it here!

4.Total Validator 4.1

Provides true HTML validation (HTML 2.0 to XHTML 1.1) using the official DTDs, plus added attribute checking. So you no longer have to put up with the limitations of the W3C validator (no type checking) and tools like HTML Tidy which interpret the standards incorrectly (they don’t use the official DTDs).

Also performs accessibility validation (WCAG, US-508), broken link checking, spell checking (5 languages), and takes screenshots using 24 browsers on Windows, Linux, and OS/X. Get it here!

5. KGen 0.2.1

KGen retrieves every words of a page and lets you know how many time they appears on her and their weight in the page (a word in the title of a page has a stronger weight than a word in a paragraph).

So, you can easily know how to optimize your pages, know what’s the secret of your competitors or simply know what’s the main subject of a webpage.

You can also select some words and transfer them to your clipboard and paste them on tag fields on your favorite social network or fill meta-keywords of your web pages.

To open the KGen sidebar : View>Sidebar>KGen. Get it here!

6. IE Tab 1.3.3.20070528

We all know how frustrating and time consuming is to edit your page especially the CSS file to make your site display correctly in IE as well as in Firefox, this Extension gives you an embedded IE in a new tab!

This is a great tool for web developers, since you can easily see how your web page displayed in IE with just one click and then switch back to Firefox. Get it here!

7. Yet Another Window Resizer 1.1

This Extension helps you view your web page in several resolutions. Get it here!

8. MeasureIt 0.3.6

Draw out a ruler to get the pixel width and height of any elements on a webpage. Get it here!

9. Clear Cache Button 0.5

Adds a clear cache toolbar button. After installing the extension, find the clear cache button in the toolbar customization panel. YES, this is an extension for the very lazy webmaster! Get it here!

10. Font Finder 0.5a

Simply highlight a single element (e.g. a paragraph or a strong tag ), right-click and select `Font Finder`, then marvel as the full CSS text styling of the selected element appears. Get it here!