GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless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.
Download the release by clicking on the link: GlimmerBlocker-1.6.6.dmg (release notes).
Safari should then download the installer:
The installer should start automatically when the download is complete :
Click "continue" and provide your password when the installer asks for it. This ensures that only administrative users can change the setup of GlimmerBlocker, so non-administrative users can't change the settings.
For some users the Installer displays the "Destination Select" pane as displayed below. When this happends, click in the blue area ("Install for all users of this machine"), then click the "continue" buttons. This bug has been reported to Apple (bug #6359800).
When the installation is done, GlimmerBlocker is automatically activated.
Because GlimmerBlocker doesn't hack Safari, its settings are not part of Safari's settings window but is located in System Preferences.
To change settings for GlimmerBlocker, choose "System Preferences..." from the Apple menu:
Then click on the GlimmerBlocker icon in the bottom of the window:
To be able to change the settings, click on the authentication lock and provide your password:
If you want to uninstall GlimmerBlocker, see the uninstall instructions.