How To Reduce Firefox 3 Load Time On Windows

firefoxchain   How To Reduce Firefox 3 Load Time On Windows Mozilla’s newest browser version, Firefox 3, enjoyed huge support when it launched, breaking a world record in the process. Over 8 million people, all over the world, combined to download Firefox 3, showing the potential of open source software to eclipse it’s mainstream rivals, mostly Internet Explorer.

With improved browsing features, Firefox 3’s performance over it’s earlier version Firefox 2 was plain to see. However, there was one issue that many users were starting to notice; the increased loading time when launching the browser.

This article will explain how to shorten the Firefox 3 load time, using free tools and your Windows command line.

Step One

Firstly, we will need to download a compression tool that will pack and reduce the size of your Firefox executable. This tool is called UPX (The Ultimate Packer for eXecutables).

Once downloaded, extract the file upx.exe and copy it to your Firefox installation directory (typically C:\Program Files\Mozilla Firefox).

folder   How To Reduce Firefox 3 Load Time On Windows

Step Two

Close Firefox if you have it running. You will now need to open a command prompt window and change its path to the installation directory mentioned above. For those who are unfamiliar with the command prompt, there is help in a small file named Open Command Prompt Shell Extension. This will allow you to open a command window from the folder in Windows Explorer (see screenshot below).

screen   How To Reduce Firefox 3 Load Time On Windows

Step Three

With the command prompt open and path changed, copy and paste the following script into your command prompt:

for %v in (*.exe *.dll components\*.dll plugins\*.dll) do upx “C:\Program Files\Mozilla Firefox\%v”

cmd   How To Reduce Firefox 3 Load Time On Windows

This command will execute the file packer which will compress your Firefox executable. Once it has finished, close all open browser windows and applications and re-launch Firefox. You should now notice an decrease in load time when starting your browser.

This tweak may be affected by any future updates to the browser but can be re-applied using the steps detailed above. Should you wish to reverse the process, you simply need to use the following script:

for %v in (*.exe *.dll components\*.dll plugins\*.dll) do upx “C:\Program Files\Mozilla Firefox\%v”

There are a few other tweaks you can employ to speed the launch of Firefox, namely uninstalling any unused Firefox Addons and changing your home page to a blank page using about:blank

Hopefully this tweak will allow you to improve load times on whatever computer you use. If you have any further tips on how to improve your Firefox load time, please leave a comment below.

Firefox photo from Flod

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Error: ‘upx’ is not recognized as an internal or external command, operable program or batch file.


Make sure you’re in the Firefox directory in the command prompt.

Matt Brian


Have you copied the upx.exe file to the C:/Program Files/Mozilla Firefox directory? Have you also directed your command prompt to the same directory?


Without wanting to sound rude your so way off the mark with this it’s untrue!

Compressing the file of course INCREASES load time because the compressed exe has to be uncompressed(albeit automatically) before execution.

The only benefit to this for end users is reduced disc footprint which is no biggie for most of us today anyway.


Agreed… this post should be renamed as it is misleading. You can reduce the size of EXE and DLL files with this program, but it certainly will not speed up load times.


Doesn’t work with either regular Firefox or 3.1b2 (yes, I made sure the command prompt’s pointing to the right place and adjusted the command to point to the right folder)

Just getting a hell of a lot of FileNotFoundExceptions


EDIT: Nevermind, typed the commands in manually rather than copypasting and it worked fine


works fine for me, surely faster :D


You need to reboot between executions or Windows dll caching will make it load faster.

This is what happens when you load firefox from an uncompressed state….

Load exe and required resources to memory.

Here’s what happens when you run Firefox UPX packed…

unpack exe and dll
Load exe and required resources to memory.

It’s completely impossible to do two things faster than one, this is not a theory of mine, this is cold hard fact!

Al Green

It is possible to speed up by compressing. It’s all due to fact that cpus nowdays are very fast disk drives havent progressed the same way. With good compression settings it can speed up.
Uncompressed (normal):
time to read full exe from slow hard drive and write to very fast ram then execute
read smaller exe from slow hdd on good cpu fast decompression to very fast ram.

in good compression ratios on reasonable decompression times compressed way will be faster


Here’s a simpler way to do the same thing: Use the AppCompactor from This does the same thing as UPX but without the command line.
From their website:” AppCompactor allows you to easily compress applications to decrease size on disk and increase performance when running from slow media”.


There are some sideeffects with this. It seems that my pages never stop loading. I cannot escape and stop the loading indicator on any page anymore, which is a huge annoyance. Yes, it’s much faster for the window to open, but in order to do any of the things I normally do, i.e. enter an address into the awesome bar, do a google search, I am experiencing enormous lag times. (And did I mention, that the loading indicator never stops?)

So, I’d say this has no practical benefit for me. It actually has some downsides, as I now have to reinstall firefox, unless there is a simpler way to revert the changes.


Oh, forgot to mention. The CPU usage for this page, which is normally at 3%, is now at 50% of my CPU capacity. Probably because it never stops loading the damn page!

Matt Brian

Thankyou for your comments. If you do find that this guide impacts your installation for the worse, be sure to reverse the process by using the command at the bottom of the article.


I found that increasing drive speed makes a big difference. I installed a velociraptor hard disk in my PC and firefox is notably faster. No brainer I guess you’d say, but I am sure firefox load time reduced by a greater percentage than my other apps did


hope i can bury the ffpreloader.


one easy way is to add /prefetch:1 to ur mozilla firefox shortcut. i m using this way dint get any trouble in loading time of firefox. In a blink firefox is ready to browse the web.


This sounds interesting. What are your before-and-after load times?

nancy bk

FF3 has been nothing but trouble for me. Bookmarks don’t work right, pages either never stop loading or links don’t work at all. It freezes all the time. The old one seemed fine. I’m back to Safari for now. At least it works.


Well – it certainly speeds it up… The shutdown is also pretty rapid. However, I am not sure that all of my add-ons are working. Certainly the tabs are not saved any more, which is really annoying, since I tend to rely on this feature to remember where I was before a shutdown… :) I am going to look at all of the other great add-ons I have installed and see if they all work and if they don’t, I shall roll the whole thing back…


for %v in (*.exe *.dll components\*.dll plugins\*.dll) do upx “C:\Program Files\Mozilla Firefox\%v”
This command doesn’t work due to spaces in path. Better go to Firefox installation directory mentioned in path and execute for %v in (*.exe *.dll components\*.dll plugins\*.dll) do upx %v

Ed Brey

Using “/prefetch” to alter the prefetcher’s hash doesn’t make sense in this application. See background here:

Ed Brey

If the time saved by reducing disk I/O does indeed overcome the decompression time, would you get the same speedup by using the file compression feature built into NTFS? Turning on NTFS compression is much easier and survives updates. Matt, for the sake of completeness, would you be willing to post code and warm timing data for out-of-the box Firefox vs. UPX vs. NTFS compression?

Additionally, if you really want to address the overall user experience, you should look at long-term usage as memory is consumed. I would expect that a downside of UPX (unless it is really clever) is that if any part of the image that the OS wants to discard in order to make memory available for caching or other processes would need to be written the swap file. For direct and NTFS compression, the write operation is unnecessary because the OS knows it can just reread the original. Ideally, you timings would run over a scripted browsing session with other apps running so that swapping delays are accounted for – not an easy task, but important: even if load time is reduced, if it a fleeting success if you must pay the piper somewhere else.


This is great ! Now v3 will load faster so that I can get to everything within it that NO LONGER WORKS more quickly. Yippee.

Jorge Rosa

Here’s another idea. FF3 startup keeps getting slower and slower, and I guess it’s because of the Awesome Bar list. I’ve tried changing (in about:config) to a lower value (500, right now) and it seems a little faster.
Anyone has tried it? With other values?



William White

Your instructions are vague for non geeks. They should be in a list. example
1. do this
2 do that etc.

You lost me at step 2
You may be a great geek but you English skills are sorely lacking. Just look at the comments and you can see this to be true.


I know it doesn’t make sense to compress the file.
But it works for me. Firefox is much faster now.


Most Antivirus-checking takes longer with UPX.
We can only benefit from UPX speed in Linux and BSD (and Mac?).

So i’ll advise a nice tradeoff using only
compact /c /s:”%ProgramFiles%\Mozilla Firefox” *.exe *.dll

Dont forget to contig or defrag afterwards. (NTFS is a cruel joke…at our expense)


This one worked fine.
I do not know the reasoning behind this.
But, it made Firefox load faster.

Don’t go by theories, go by conviction.

Jack skelly

Firefox used to take 1 to 1.5 minutes to load. I have XP and found that adding more ram took care of alot of problems. Firefox now loads in about 15 seconds.