Select alternate stylesheets with a page action menu
Allows you to pick between alternate stylesheets, if the page offers them. The page action only appears for pages with alternate stylesheets.
For an example of a page with multiple stylesheets, see: http://www.w3.org/Style/Examples/007/alternatives (I used this for the screenshot, but cut down the list of styles to fit.)
Source code (MIT-licensed) and issue tracker at http://github.com/decklin/style-chooser.