Firefox have a great ability to tag web page. We can use tags to put pages into the same category. We have open each bookmark in this folder/catalog, but why not open all pages with a given tag?
For example: I'm web developer, so I tag development page as "Project Evil" and also documentation pages as "Project Evil". I close each tab in browser and go home. When I decided to work on "Project Evil", then I only write "Project Evil" into awesomebar and enter into "open each tab with this tag" option.