RSS is great technology, but one of its shortcomings is that it doesn't always represent all of a site's content stream. Many times there are parts of a news or content site that change either through an editorial hand, or with items chosen by users. A new Firefox add-on called AlertBox helps track these "scraps" of content, and can be used to keep an eye out for any changes. This includes things like price changes, edits or updates to a news story, and the top stories on content sites.
To make sure it's not looking for activity on an entire Web page, AlertBox is designed to let you grab bits and pieces of any site--not the entire thing. Once installed, you can summon it by clicking the little bell shape in the bottom corner of the browser, or using a keyboard combination. It then pops up with a selection screen that, similar to Apple's Web clips widget, lets you pick what part of the page you want it to track. You can then choose how often you want it to check for future changes in increments of two minutes, up to one day.
AlertBox's way of tracking new content is an in-box-style counter down in the bottom of your browser. When clicked, it takes you to a page of Web clippings that are constantly updated with whatever the latest text is of the page elements you had selected. To be honest, this part of the add-on could use a little work, as it's just a text rip that loses all of the formatting on the page. And all of these alerts are housed not in the cloud, but on your local machine, which has two big downsides: One is that you need to have Firefox going at all times for it to alert you. The other is that you can only access those alerts on that particular machine.
Faults aside, I really like the idea of creating a simple in-box of changing content that does not rely on RSS. I think this, with a little bit of archiving to let you track changes in content throughout the day (like Web archiving service Iterasi does), would make for a very useful alternative to widget start pages and feed readers.