I've reinstalled Windows 7 beta and Linux several times lately, trying to find the best dual boot mix on my notebook (in terms of partition management). It's a good time to reflect on what I really use. I've found that with a fresh, empty Firefox, without peeking into the lengthy addon list on my desktop machine, I go and grab the following right away:
The first four need no introduction here, but Wired-Marker seems rarely mentioned. It's a highlighter that stores the highlights locally. It doesn't capture the whole page (unlike scrapbook), but the highlights are there when you revisit the page. I use it when I want to highlight parts of a page that changes.
The obvious question is, if the page changes, how does Wired-Marker keep track of the exact locations of my highlights? I don't know the specifics. According to my experience, however, Wired-Marker does a pretty good job keeping tab. The only exception I know is, if a change is made in the same paragraph of a highlighted part, and is ahead of or overlaps with the highlighted part, then Wired-Marker loses track of that specific highlight. But other highlighted parts in the same page--either in other paragraphs or in the same paragraph but are before the change--won't be affected.
This isn't too bad for my purpose. Take Postfix Configuration Parameters
page for example. It's a very long page since it documents every tweak you can make with Postfix. It changes quite often because the author keeps the references well updated (among the best in the industry); capturing it locally doesn't make sense. Most of the changes are nonetheless new parameters or new options for existing parameters. IOW, they usually come as new paragraphs. Wired-Marker highlights, as long as they don't span many pagagraphs, are thus quite safe.