Also for merging webpages on the fly as you surf around the web in your Firefox browser, and exporting them as a single HTML file that you can copy to your reader later on, try the ScrapBook Firefox plugin:
https://addons.mozilla.org/en-US/firefox/addon/427
For advanced users of Linux (some command line interaction needed), I used the HarvestMan web crawler (
http://www.harvestmanontheweb.com/) to get all the html pages for a free-online ebook that I wanted to read, then I used HTMLDOC (
http://www.htmldoc.org/) to make a nice pdf from the html. The HTMLDOC is so good, that it created a pdf the table of contents from the master html page, which worked perfectly in my e-reader.