Net Panel

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Revision as of 22:20, 15 January 2014 by Sebastianz (Talk | contribs) (Enhanced description of aborted requests)

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Net Panel

The main purpose of the Net Panel is to monitor HTTP traffic initiated by a web page and simply present all collected and computed information to the user. Its content is composed of a list of entries where each entry represents one request/response round trip made by the page.

Options Menu

This menu is reachable via the little arrow in the panel tab ( NetPanelOptionsMenuArrow.png ) or by right-clicking on on the panel tab (since Firebug 1.9).

Option Preference Description
Enabled/Disabled Enables the Net Panel
Disable Browser Cache browser.cache.disk.enable
Disables/enables browser HTTP cache.
Show Paint Events extensions.firebug.netShowPaintEvents Specifies whether DOM paint events shall be shown as vertical lines inside the Net Panel

Note: Due to a security issue these events are not sent to web content anymore by default. You need to set dom.send_after_paint_to_content to true in order to see them.

Show BFCache Responses extensions.firebug.netShowBFCacheResponses Specifies whether HTTP responses coming from the BFCache should be displayed.

For more info about tweaks available in Firebug please see the full list of preferences.

Panel Toolbar

Break On XHR

Clicking the "Break On XHR" button ( Break On XHR Button.png ) enables a listener for XMLHttpRequests. If an XHR is made then, the debugger stops the script execution immediately and jumps to the Script Panel.


Removes all entries of the list of requests.


When this option is enabled, the entries of the requests list are not deleted when reloading the page. Instead the are grouped by page request, which means, when reloading the page several times you will get several request trees having the page title as root.


There are several buttons for filtering the current list of requests for giving a fast overview over the files you want to see. Following there's a list of the currently implemented filters:

Filter Description file types
All Displays all requests All
HTML Limits display to markup files (X)HTML, XML, MathML, RSS, RDF
CSS Limits display to CSS files CSS
JavaScript Limits display to JavaScript files JS
XHR Limits display to XMLHttpRequests XMLHttpRequests
Images Limits display to image files JPEG, PNG, GIF, BMP
Plugins Limits display to Flash and Silverlight files SWF, XAP
Media Limits display to media files MP3, Ogg, WAV, MIDI, WebM, MPEG, FLV
Fonts Limits display to font files WOFF, TTF, OTF

You can also select multiple filters by holding down Ctrl / while clicking the filter buttons. This feature was added in Firebug 1.12.


You have the possibility to search inside the different requests. Thereby besides the general options for case sensitivity and regular expression search you can optionally also search inside the request bodies.

Request List

The main part of the Net Panel is the Request List. When the Net Panel is activated and a page is loaded it starts filling with all HTTP requests made by a page. Each entry displays basic info about the request and a graphical Timeline that depicts load phases in time. The following is a list of information, that is displayed for each request:

  • HTTP request method
  • HTTP response code and description
  • Requested file name (shortened; hovering it shows the entire URL)
  • Domain name from where the response came from
  • Size of the response (compressed size in case of compressed responses)
  • Graphical Timeline and load time info

Depending on their loading status and source the requests are displayed differently:

Filter Description Example
Normal finished requests Requests fetched from the server NetRequestFinished.png
Loading requests Requests currently being fetched from the server NetRequestLoading.png
Cached requests Requests with response coming from the browser cache (HTTP status code 304) NetRequestCached.png
BFCached requests Requests with response coming from the BFCache NetRequestBFCached.png
Erroneous requests Requests, which returned an HTTP error (HTTP status code 4xx or 5xx) NetRequestError.png
Aborted requests Requests, which were aborted by the client NetRequestAborted.png

Besides that there is a summary at the bottom of the Request List. This summary contains info about the total number of requests, the total file size and the total page load time.

Request & Response Details

Every request entry can be expanded by clicking on the left hand twisty in order to see additional info. It's important to note that the entry actually represents both: the request sent to the server and also the response coming back. No matter if it comes from the server or the browser cache, one request-response round-trip is represented by one entry in the list. There are several tabs shown for each request. Depending on the request method and requested file type there are additional tabs with further information. Here's a list of the tabs shown for the different requests:

Tab Restriction Description
Headers - Lists the request and response headers of the current request
Response - Displays the contents of the response unformatted (as they came from the server)
Params GET request Displays the URL parameters
Post POST request Displays the POST parameters in a formatted way (depending on the Content-Type of the request) and the raw data inside the Source section
HTML HTML files Displays the rendered HTML output
JSON JSON files Displays the JSON data in a formatted tree structure similar to the DOM Panel
XML XML files Displays the XML data in a formatted tree structure similar to the HTML Panel
Cache Cached files Lists cache information to the current request

There can be also other tabs coming from Firebug extensions. An example is a Cookies tab that shows all sent and received cookies for a request. This tab comes from the Firecookie extension.

Cache Info

Some files are fetched from the browse cache. They can be recognised by the response status "304 Not Modified". The Cache Tab includes the following information:

Info Description
Last Modified Last time the cache entry was modified
Last Fetched Last time the cache entry was accessed
Expires Expiration time of the cache entry
Data Size Cache entry data size
Fetch Count Number of times the cache entry has been accessed
Device ID for the device that stores this cache entry


One of the most useful features for debugging page load performance is a request Timeline. The Net Panel uses this graphical representation to show request load in time together with timing data.

Request Timeline

Every request-response round trip is shown as horizontal bar in the Timeline and is composed of several phases, represented by different colors. Hovering a Request Timeline offers more detailed information about the timings of the different phases.

Value Display Description
Time spent in a browser queue waiting for a network connection (formerly called Queueing)
For SSL connections this includes the SSL Handshake and the OCSP validation step.
DNS Lookup
DNS resolution time
Elapsed time required to create a TCP connection
Sending request headers
Waiting for a response from the server
 (from cache)
Time required to read the entire response from the server (and/or time required to read from cache)
'DOMContentLoaded' (event)
(blue line)
Point in time when DOMContentLoaded event was fired (since the beginning of the request, can be negative if the request has been started after the event)
'load' (event)
(red line)
Point in time when the page load event was fired (since the beginning of the request, can be negative if the request has been started after the event)
'MozAfterPaint' (event)
(green line)
Point in time when a MozAfterPaint event was fired (since the beginning of the request, can be negative if the request has been started after the event)
Time stamp
(olive line)
Time stamp created via console.timeStamp()

Waterfall Graph Time Extent

In order to keep the X axis (time) in sensible extent, the waterfall graph breaks the time and starts displaying new requests that start later (in the page life) again from the beginning. In other words, a request, that starts after a predefined period of time (1s by default) since the previous request finished, starts from 0 time of the graph again. This avoids endless extension of the X axis, which would make the graph less readable. There is a preference extensions.firebug.netPhaseInterval allowing you to set the gap in milliseconds, after which the time break should happen. If set to 0, breaking doesn't happen at all.

Breakpoint Column

Setting breakpoints

The Breakpoint Column allows you to set breakpoints for XMLHttpRequests. By clicking on it a breakpoint is set for the request. Clicking it again removes the breakpoint again.

Breakpoint conditions

You can create a conditional breakpoint by right-clicking a breakpoint. Doing so opens the Breakpoint Condition Editor:


There are variables available, which can be used within the expression:

Variable Description
$postBody Response content of the POST request
<parameter name> Parameters used within the POST request

Context Menu

Request list header

Option Description
URL Toggles the display of the column for the URL of the requests
Status Toggles the display of the column for the HTTP status of the requests
Protocol Toggles the display of the column for the protocol of the requests
Domain Toggles the display of the column for the domain of the requests
Size Toggles the display of the column for the size of the responses
Local IP Toggles the display of the column for the client's IP of the request
Remote IP Toggles the display of the column for the server IP of the request
Timeline Toggles the display of the column for the Timeline of the request
Reset Header Resets the column display to the default


Option Context Description
Copy Location all requests Copies the URL of the request to the clipboard
Copy URL Parameters requests with URL parameters Copies the URL parameters of the request to the clipboard
Copy Location with Parameters POST requests Copies the URL including the parameters to the clipboard
Copy POST Parameters POST requests Copies the POST parameters to the clipboard
Copy Request Headers all requests Copies the headers of the request to the clipboard
Copy Response Headers all requests Copies the headers of the response to the clipboard
Copy Resonse Body text file requests Copies the response body to the system clipboard
Copy as cURL all requests Copies the request as a cURL command to the clipboard (added in 1.12)
Open in New Tab all requests Opens the resource in a new browser tab (uses the same HTTP method as the original request)
Open Response in New Tab text file requests Opens the response in a new browser tab
Stop Loading loading requests Stops loading the request
Resend all requests Sends the request again
Use in Command Line all requests Focuses the Command Line and makes the request available as $p.
Inspect in Script Panel JavaScript requests Allows to inspect the requested JavaScript inside the DOM Panel
Inspect in CSS Panel CSS requests Allows to inspect the requested style sheet definition inside the DOM Panel
Inspect in DOM Panel all requests Allows to inspect the request inside the DOM Panel
Break on XHR XMLHttpRequests Toggles the breakpoint for the request
Edit Breakpoint Condition... XMLHttpRequests with set breakpoint Opens the dialog for setting a conditional breakpoint

Copying a request as a cURL command

cURL is a command line tool for transferring data with URL syntax. Firebug's Copy As cURL command recreates the HTTP request (including HTTP headers and query string parameters) and copies it as a cURL command string to the clipboard.
The string can be pasted into a terminal window to execute the same request or for example pasted to a client that supports cURL.
In cases where the server serves compressed responses the preference net.curlAddCompressedArgument can be set to true and Firebug will add the --compressed argument to the generated command string.

See also