I was hoping someone with more expertise would step up, but since no one has, here's what I do with Firefox:

1. I run a search on Craiglist. In some cases, I use Boolean logic to catch multiple related things in one search (e.g., trumpet or cornet, country or western).

2. On the results page, I click on the "RSS" button on the lower right hand corner of the page.

3. A menu shows up at the top of the page showing "Subscribe to this feed using", along with a drop-down menu.

4. From the drop-down menu, I choose "Live Bookmarks". Then I'm given the choice of naming the bookmark and choosing the folder in which it will be created.

5. In regular use, when I left-click on one of those bookmarks (or hover over it if it's in a drop-down list of bookmarks), then a list appears showing all the results from that feed. If I right-click on a bookmark, one of the options is to "Reload Live Bookmark".