Stack OverflowFirefox add-on to simulate slow internet connection or limit bandwidth?
[+129] [13] Greg
[2009-01-23 16:07:08]
[ download connection firefox-addon performance bandwidth ]

Is there a Firefox add-on available that will simulate various connection speeds (especially when testing from http://localhost)?

I know there are standalone applications to do it, but I'd rather have a plugin.


Edit: Thanks to @UselessAdmin - FirefoxThrottle has now been updated to work on localhost!

250 points for a quick google search? - cjk
(5) @ck if you have an answer, write it below and get an easy 250 points - Greg
(3) I sure hope it's not a "quick google search," because I've attempted that numerous times just getting my answer formulated. - Jonathan Sampson
By slow do you mean low bandwidth or high latency? - Chris Upchurch
Jonathan's answer should work fine. Just use your local IP address. - geowa4
@George IV it doesn't. It says in the plugin documentation (and I've tested) that it doesn't work on localhost. Using another IP doesn't trick it either. - Greg
Greg, have you found anything new? I need to test on localhost, or something close to localhost. - Yar
(3) Could this question be reopened? Firefox Throttle appears not to be available for download from Firefox Add-ons. - JonathanHayward
Firefox Throttle doesn't appear to be online anymore. - Jeremy Ricketts
Get your cable modem from Time Warner, and you won't have to simulate a slow connection, it will just happen. - Paul Tomblin
Perhaps what you actually need is the YSlow addon for FireBug? - slf
[+131] [2009-01-23 16:13:31] Jonathan Sampson [ACCEPTED]

Firefox Throttle [1] Now works on localhost

"Firefox Throttle is a small plug-in for your favorite Web Browser, that allows you to cap download/upload rates and monitor current bandwidth utilization. "

Internet Explorer Throttle [2] (As of 2010/02/23, still doesn't work for localhost)

"IE Throttle is a small plug-in for your Microsoft Internet Explorer, that allows you to cap download/upload rates."


(4) The Mozilla homepage for the addon is at: - TravisO
@TravisO - I just thought to use that link instead too. Thank you for the suggestion though. - Jonathan Sampson
(1) Hmm I can't get it to work... I've unchecked "automatically exclude all local networks" but it's still not throttling localhost (internet sites are throttled OK though) - Greg
Read the comments and it seems it doesn't work on localhost :( - Greg
@RoBorg, perhaps you should consider throttling with your local installation of Apache? - Jonathan Sampson
Wouldn't that involve restarting apache every time I wanted to toggle the throttle on/off? I really want something faster than that. If that plugin worked for localhost it would be perfect - single click to toggle... - Greg
@RoBorg, I agree. A plugin for localhost would be awesome, but if it doesn't exist, Apache might be the way to go. I'll continue looking though, as this would benefit me too. - Jonathan Sampson
@RoBorg - Could you setup multiple virtual hosts with Apache, and specific throttles for each? localhost, localhost_56k, localhost_DSL etc? And point them all to the same directory? - Jonathan Sampson
@Jonathan Sampson - I have about 15 virtual hosts already - setting up different speeds for each one would be a pain, but not impossible. - Greg
@RoBorg - It was just an idea. I think I might give that route a shot myself. I currently only have a couple. I will continue to look for a more simple solution, and I'll post back here when/if I find it. - Jonathan Sampson
@Jonathan Sampson Cool, thanks. - Greg
(1) :( - Firefox Throttle doesn't work on Linux! - a_m0d
(2) This solution is not quite accurate. It will simulate limited bandwidth, but it does not simulate latency. Very small requests will still be responded without delay. - Adrian Grigore
(6) The add-in seems to be removed from the Mozilla site. At the time of writing it's still available from the Mozilla ftp site:… - Zidad
Used @Zidad's link. Tricky to get localhost throttle working, but if I enabled/disabled localhost & localNetwork options from the status bar a few times, it eventually worked ok - Brian Bishop
It is removed from Mozilla, but still available at the link in the answer. However, it isn't possible to deactivate it without errors. I'd recommend the answer below. - Znarkus
[+62] [2009-01-27 11:00:52] markus

1 Linux

Traffic Control

On every modern Linux system you will find the tool "tc" (traffic control).


For several *NIX distros there are packages called ' iprelay [3]'.


For example Debian you could do the following:

$ iprelay -b2500 8000:localhost:80
# Point browser at http://localhost:8000

and you can see your website creations as a poor modem user would...


or a link for an Ubuntu package:

2 OS X

The original iprelay Perl script found at Gavin Stewards website [4] works on OS X out of the box.

3 Windows

Another tool which works on Windows: Internet Speed Simulator [5]


The question stated, "I know there are standalone applications to do it, but I'd rather have a plugin."... - Nik Reiman
(19) it might help someone else, stackoverflow is a wiki after all. - markus
(1) iprelay works great. Thank you very much. - pi
Website for ip_replay: - MitMaro
(1) tc - traffic control is also a handy and powerful alternative. In you can see how to put latency on a loopback device. - Mark Raddatz
Thanks a lot, It helps on *nix. - CoolGoose
Yes, it helped me. I had used this before but couldn't remember the name. - Matt McCormick
[+18] [2009-01-28 13:15:49] Kristof Neirynck

The "Charles Web Debugging Proxy" has no problem throttling localhost. It works on windows, mac and linux. The trial version is fully functional and a licence costs only $50. I highly recommend it.

[+15] [2009-01-29 07:20:26] AndrewDotHay

Fiddler can similulate slow modem connections:

Here's how to modify the delays [1] in the request and response.

Here's how to use Fiddler with Localhost [2].


[+14] [2009-01-28 16:23:05] bike-fan

The solution I use is a combination of Firefox throttle [1] and Sloppy [2]

  1. Install FirefoxThrottle. This will display the speed in the Firefox status bar.

  2. Now in Firefox go to the address you want to throttle and get the EXACT URL.

    • A lot of websites have redirects which can throw sloppy off.
    • Go to the start page for the site you want to throttle.
    • Copy the exact URL into the windows clipboard. The exact URL will include the http:// and the www parts if they are part of the URL,

Example: I'm in Canada so if I type "" in the FireFox URL it actually takes me to

  1. Start Sloppy (it is a Java webstart) so just double click the sloppy.jnlp file

  2. Now paste the URL into sloppy (i.e. Paste the entire "" string).

  3. Firefox will take you to which is a throttled version of the site.

  4. Firefox Throttle will display in the Firefox status bar the speeds you are getting.


[+8] [2009-05-05 16:55:06] UselessAdmin

Due to overwhelming popular demand Firefox Throttle has been updated, it can now throttle localhost connections.

Excellent news! I'll try it out ASAP - Greg
[+7] [2009-01-27 11:07:01] DrJokepu

I think you would be better off by using a purpose built proxy as it would work in all browsers and/or any other applications. So I think you should have a look at Sloppy [1].

Basically, all you need to do is launch Sloppy, enter the address of your site and then it will open it in your default browser and simulate a dial-up speed. As a plus side, it's written in Java so it would work on Mac or Linux as well.


[+7] [2009-01-27 11:16:45] Jenko

Use NetLimiter [1] to limit your internet bandwidth upload/download per program.

Simply checkmark the Incoming/Outgoing limit checkbox next to Firefox, type in a speed limit in the current units (Kbits/KB per sec/kbits per sec).

Firefox's connection speed is limited to your setting so you can simulate slow download speeds, etc!


[+5] [2009-01-27 15:27:03] phloopy

Adding to DrJokepu's [1] answer, set up Sloppy [2] (or a similar proxy) then use the FoxyProxy [3] plugin for firefox, which supports sending particular addresses through particular proxies, as well as easy toggling if you don't want to use them at all.


Hehe, Sloppy... Lol. - Jonathan C Dickinson
[+4] [2010-02-05 07:41:35] PCheese

Here's an easy and configurable non-proxy solution for Mac users that works across browsers. It installs as a preference pane.

speedlimit home page [1]


ThankYouThankYouThankYouThankYou - Jeremy Ricketts
[0] [2009-05-30 05:00:35] community_owned

Run a proxy server, config firefox to use the proxy server, and control the bandwidth on the proxy server.

[0] [2009-01-27 15:35:13] Ates Goral

There could be a way to trick the plugins mentioned in @Jonathan Sampson's answer [1] to do throttling also for your local server.

If you have a high-speed connection and you're behind a modem/router that you are willing to configure (one time set up):

  1. Add an entry in your hosts file to point localhost to your external IP (that hopefully doesn't change much). You mentioned that you're using virtual hosts. You should add them as well.
  2. In your router, map external accesses to port 80 (or whatever) to port 80 of your local machine.
  3. Hopefully, the plugin won't think that the server you're trying to access is on a local IP and therefore won't throttle the connection.

Assuming your external IP doesn't chance all the time (especially if you're in an office with a dedicated line), this solution will help you to use those plugins, with a one-time or one-in-a-while setup in your modem/router.


[0] [2009-01-30 09:26:28] Otherside

You might be able to use the DelayPools [1] feature from Squid proxy [2].

Another possibility is the bandwidth throttle [3] feature from Charles Proxy [4]. Charles Proxy includes an Add-On for Firefox which will automatically configure the proxy settings.