For this test, I’ve set up a server (1 intel processor/512MB ram/12MB video memory) with Ubuntu Server 10.10 (32 bit).
I could test some static resources but nowadays, particularly all websites are dynamic ones so I’ve installed Mysql/PHP and of course Apache2, all with the default settings, on my server.
Next, I’ve downloaded WordPress and installed it on the server, changed the appearance to ‘pixel theme’ and added a few posts with images in.

Time to test

I’m not going to do fancy stuff, the module is installed with the default options enabled and I’ll just use Firebug to do the tests.

First the tests without the module installed:

The results with the module installed:

Mod_pagespeed_statistics:

Conclusion:

• The amount of requests have been reduced in this case with 2 (-15%)
• The pagesize has been reduced with 5.2KB (-1.5%)
• The loadtime is shorter when mod_pagespeed is enabled (-13%)

The 50% profit claim is a little bit optimistic because the bottleneck in the pageload is the dynamic content and that’s a part where this module doesn’t do anything. But in general, the module does a reasonably good job. I get a 13% profit with mostly default values, a good configured server should propably even do better.
I will definitely test this further and maybe put it one day on a production server.

The config used in this test looks like this:

<IfModule pagespeed_module>
    SetOutputFilter MOD_PAGESPEED_OUTPUT_FILTER
     ModPagespeed on
     ModPagespeedUrlPrefix "http://localhost/"
     ModPagespeedFileCachePath "/var/mod_pagespeed/cache/"
     ModPagespeedGeneratedFilePrefix "/var/mod_pagespeed/files/"
     ModPagespeedRewriteLevel CoreFilters
     ModPagespeedDomain localhost
     ModPagespeedEnableFilters add_instrumentation
<IfModule>

My full configuration file can be downloaded here.

If you want to log in like this, Firefox will show you a dialog where you have to confirm that you want to login directly into the website.

This is done for some securityreasons because it’s possible, like the dialog says, to trick a user to the wrong site.
Take for instance the following url:
http://www.eek.be&login:password@example.com/badsite
This url looks perfectly valid but if you have a good look at it, you will see that the url is not one of eek.be but one of example.com. So when a user clicks this link, it will be redirected to a page he didn’t expected or worse, a site that looks like the page he thinks he expects which asks him for his creditcard/username/password/…

So this built in security in Firefox is a very good case.
But in some cases, you just want to login to a site without that annoying alertbox. Luckily, In firefox, it’s possible to configure this option.
Go to the options in Firefox by surfing to:

about:config

You should get a warning but you can proceed without any concerns.

Now you have to rightclick inside the optionsscreen and choose new->integer
A popup shows up and you have to fill in the optionsname

network.http.phishy-userpass-length

secondly, you have to give a value to the option.
In this case, the value means how many characters a login can have before the dialog appears. By default it’s 1 in Firefox. In this case I change it to 100 which is enough in most cases.
If you want to disable it always, you have to set the integer to 255.