In the article "Using Firebug for troubleshooting Browser issues" the "Net" panel is described as a good performance analysis tool. This article describes how to export the Net panel from both Firebug and Chrome HTTP tracking tools to an HTTP Archive (HAR) file so that the analysis can be documented and passed to other analysts for detailed discussion and analysis.
In Firebug the NetExport extention must be added in order to enable export of the Net panel. Go to https://getfirebug.com/releases/netexport/ and click on the latest release to install the extension. When you next open Firbug a new Export button appears in the Net panel tool bar. Click on the Export button and choose "Save As..." to save the HAR file to your file system.
In Chrome, the ability to export the Network panel is built in. Open the Developer Tools, click on the Network panel, then right-click anywhere within the panel and choose "Save as HAR with Content" to export the panel to the file system.
The HAR file viewer
To view the HAR file go to http://www.softwareishard.com/har/viewer/:
Then drag and drop the .har file onto the page: