Is your web page loading really slowly?  Are you wondering if it is the javascript, the images, your files, or maybe something else that you have not thought about?

Firebug has a feature that breaks down the load time for loading your web page.  Launch Firebug from your Firefox browser and click on Net.  From here you can select All and see a breakdown of what is loading on your site.  The All selection shows everything - from you .css files, your .js files, your images files, etc.

You may want to compress your javascript files, or find a way to combine all of your js and stylesheets into one minimized file.  The usual culprits are large image files - such as huge .jpg files and the worst are .png files - they can be huge.

This Firebug feature also shows you the size of each file - so you can see if something sticks out as an unusually large file size.

screenshot-firebug-loadtime

You can also choose other tabs under NET and focus on certain filetypes, such as only focusing on the .js files. Another useful aspect of this feature helps with debugging - to be sure that your .js files are loading in the correct order to function properly. Say your fancy-schmancy jQuery prograpm isn't working right - then you find out that it was loading before the jQuery library files. This is a good place to diagnose issues such as that.

To find out more on this particular feature - visit getfirebug.com/network

To find out more about Firebug itself - visit their WIKI