OK, so the state of play is this: I have a toolbar, it incorporates the majority of searches for linguistics, many paid-for dictionaries (like OED, Oxford Research Online, ordnett.no, etc.) and some search engines.
I am currently struggling with the preference system, which is integrated with the Firefox preferences system, and is basically a tree with collapsable views, and checkboxes for activation of reseource. The toolbar therefore allows a user to create their own sets of resources. This means that the toolbar can be used by people studying more than one subject (which is the norm for arts/humanities students), and makes the toolbar more flexible for interdiciplinary stuff.
Although the basic search functionality of the toolbar is nailed, I reckon that it is best to have some sort of extensible system that imports search data from an external source (like an RDF file). This will mean that the resources can be updated easily (and even provided directly online — although this approach probably has more drawbacks than I can even imagine).
The preferences system: I wonder if the toolbar should also be adaptable structurally — i.e. should a user be able to change the order, folder structure and general arrangement of files in their toolbar?
I am also thinking about implementing some way of allowing a user to include their own resources; actually, I consider this a must, but I wonder how to make this consistent with the rest of the toolbar.
In the original snapshot, I made a few shorcuts to bring the toolbar online, these are being re-written to provide a more extensible, re-usable framework for later development.
The toolbar will be posted both as a package for Firefox and in source, and registered with addons.mozilla.org.