Shouldn't you be looking at the ScrapBook plug-in for FF? Or, as alternatives, NetSnippets, Evernote or Surfulater, the first two of these having completely free versions, and all mentioned (frequently) elsewhere on DC, notably the General brainstorming for Note-taking software thread? I see you've posted there, but it's an awful long thread to work through.
Yes, a long thread and a lot to think over ...
Thanks for the suggestion for Net Snippets - I'd seen it but not tried it.
But to clarify my point was basically about adding some more functionality to the existing Bookmarks Manager within firefox; in particular the ability to swap quickly between a number of customized bookmark pages - i.e. manipulating lists of bookmarks. The idea is just an offshoot of the original request ...
The beauty of the bookmark pages in FF (as they are) is that they are very easy to edit in using cut/paste, drag/drop. You can sort through 100s of bookmarks and re-order them into folders, move folders around, insert separators etc in a few minutes. (unlike IE where you are dealing in hundreds of individual link files written to disk)
You can chop a page down as desired to a selected list of URLs and export the page to another folder and later send the page(s) to other FF users. They can be loaded easily into other Gecko based browsers like K-Meleon.
FF also has a nice feature where you can just drag a link from the navigation box straight across to your bookmarks side bar and place it anywhere you wish on the list (which I'm sure most people are aware of).
As I see it, having the ability to simply swap between a number of custom URL lists in FF (in the form of multiple Bookmark pages) would be a real bonus, adding extra goodness to what is already there. Everything stays in FF - no other software required.
A bit OT here but as for web page capture, DL management and archiving I've been using Offline Commander http://www.offline-commander.com/index.shtml
for over 4 years now for various research and multimedia projects. It's proved to be the most practical solution I've found. It does the one thing and very well IMO. All your project archives are basically stand alone exe files - all neat and tidy and easy to search.