GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless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.
Removed expansion of simple hostnames into the www.*.com version as Safari now has unified URL/search bar and it made Chrome think there always was a www.*.com host for the entered word. By report from Daniel Shannon.
Support content-encoding = 'none' as a workaround for some buggy sites ('none' is not a valid value). By report from Cecilia.
Workaround for (proxy) servers which use "Transfer-Encoding: chunked" for content-less responses such as "304 not modified" and expected the client to read the empty response, including the trailing zero-length chunk.
Support for adding/overwriting JavaVM args using /Library/GlimmerBlocker/JavaArgs.plist. By suggestion from Daniel Thill.
Support for java.net.preferIPv6Addresses. Suggested by Niklas Bölter.
Upgraded Rhino to latest git version. By suggesion and info from Zearin.
Minor improvement: Use charset in content-disposition for Safari 6 and later.
This improves naming of movie downloads when the movie title contains non-English letters or special Unicode characters.
Version 1.5.2 was released 2013-05-18