This extension is compatible only with Firefox 3.0.x, a branch which reached end-of-life on 24 April 2012. It could probably be made to work on some newer versions, but certainly not any that are still supported. I might update it for Pale Moon or Waterfox someday but I wouldn't hold your breath.
Winestripe is a repackaging of the Winestripe default theme from Firefox 2 in a Firefox 3 extension.
Download and install the xpi from the releases page.
The Winestripe theme assets and code (by Mozilla and Firefox contributors) and all original code in this extension are available under the Mozilla Public License 1.1.