I have been recently working on an extension (code name HTTP Monitor) that can be used to intercept HTTP traffic of a browser tab. The extension is based on Firebug's Net panel and is on its way to be embedded in Firefox by default.
This post explains how to use HTTP monitor to intercept HTTP traffic on mobile with Fennec (Firefox for Android) installed.
Monitor HTTP traffic on mobile
HTTP Monitor is Firefox extension and so, you need Fennec installed on your mobile phone. Fennec is compatible with Android 2.2 and above devices.
In case of remote debugging you need to install HTTP Monitor extension on both sides: client and server. In this case, we want to monitor HTTP traffic on mobile (server) and check all results on desktop machine (client).
There are couple of preferences you need to set through
extensions.httpmonitor.serverMode set to true (you need to restart the browser)
extensions.httpmonitor.serverHost set to IP address of your phone (10.0.3.110 in my case).
In order to find IP address of your phone follow Settings > Wireless Controls > Wi-Fi settings and tap on the network you are connected to. It'll pop up a dialog with network status, speed, signal strength, security type and IP address.
As soon as you are all set (extension installed and preferences set) you can start Fennec on the phone and load a page. In my case I loaded
Start also Firefox on your desktop machine and open HTTP Monitor console: Web Developer -> HTTP Monitor. There should be a Connect Me button at top left corner of the window.
Both the IP address and port number comes from preferences. Connect your phone and click the other: Select Tab button to pick a tab opened on your phone.
Now reload the tab on your phone and watch the result on the desktop!
Mobile HAR File
Here is an online HAR file showing mozilla.org page load on Samsung Galaxy Nexus: