Installing lots of extensions on a single Firefox installation can turns Firefox into a bloated, heavy and memory hogging browser for web surfing. If you love to use Firefox in your web development and design, you should install the addons for web development to a separate Firefox installation, not the one that you use for daily web browsing.

I recommend you to download Firefox Portable to do this. However, by default, you cannot run Firefox Portable with a local copy of Firefox side by side. Here are the steps to force Firefox Portable to run side by side with a local copy of Firefox:

1. Browse to the installation directory of Firefox Portable. Browse to Other\Source. Copy FirefoxPortable.ini to the root folder of Firefox Portable installation directory (where FirefoxPortable.exe is located).

2. Edit FirefoxPortable.ini that you copied. Locate AllowMultipleInstances. Change the default value of AllowMultipleInstances=false to AllowMultipleInstances=true. Save the changes.

Now you can run Firefox Portable simultaneously with a local copy of Firefox. Here are a few addons that can turn your copy of Firefox into a browser for web development:

1. Firebug – The best Firefox extension for web development. Firebug will let you to ‘edit’, debug, test JavaScripts, monitor CSS and HTML of a web page live from Firefox. A must have addon for web developer.

2.  Web developer – This extension adds a menu and a toolbar to Firefox with a collection of web developer tools. However, most of the tools you can find in web developer is available in Firebug.

3. ColorZilla – ColorZilla is a simple eyedropper for Firefox, so you don’t need any external program to color picking on a web page.

4. FireFTP – FTP client in Firefox, without the need to have external FTP client to transfer files to your web server. Supports proffesional FTP client features such as SSL/TLS/SFTP, UTF8 characters, integrity checks for transfers, IPv6 and many more…

5. MeasureIt – This addon enables you to draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.

If you have trouble to install addons to the Firefox Portable, try to download and save the addon file to your system first, then drag the addons files into Firefox window to install them.

[Firefox Portable]