Installing
As usual put the source code in a file called plugin.quickgallery.php and put it in a directory called fp-plugins/quickgallery/
Usage
[gallery=images/subdirectory-containing-images otherparameters..]
where otherparameters is whatever [IMG] parameter you like. I suggest a scale=NN% or a height=NN to get a popup. Please notice that if you have lightbox plugin installed you'll get a lightbox slideshow :)
galleries are automatically wrapped in a div with class=“img-gallery name-of-gallery” where name-of-gallery is a sanitized version of the string images/subddirectory-containing-images; in most cases it will look like imagessubddirectory-containing-images all lowercase, with spaces turned into slashes and non-ascii/accented characters stripped out/converted to plain ascii.
see your generated html in your browser to know how the string looks like
to style every gallery just use .img-gallery{ } in your CSS