GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless you resort to install custom SSL certiticates on the client.
You should use a browser extension instead.
It was made as a hobby project during 2007-2008 by Peter Speck. It features both a custom http server and http client and a Mac OS X control panel.
GlimmerBlocker did not only block requests but also allowed for adding custom css and javascript to the pages. It also allowed for modification of the page html before the browser receives the html, which made some modifications much easier than DOM based modifications.
GlimmerBlocker cannot be installed onto your iPhone or iPod, so you cannot use GlimmerBlocker when surfing using 3G. But when you are at home and using wifi, iPhones and iPod Touch can use GlimmerBlocker running on your Mac.
Open System Preferences, choose GlimmerBlocker, select the "Network tab", and check the option to: "Allow iPhones ... to use GlimmerBlocker on this Mac."
On your iPhone/iPod open the "Settings" built-in application and select the "wifi" option:
Click the blue button to change network setup:
Scroll down to the botton, and select the "Manual" tab in the "HTTP Proxy" section. Type in the ip-address of your Mac and specify 8228 as the port number:
To find the ip-address of your mac, open the "Network" System Preferences Panel.