Fancy saving money? From cheap flights to online auctions, price monitoring to comparison shopping, these Firefox add-ons can make your money go further. And of course, they're free.

1. Firefox Companion for eBay
The Companion shows auctions in the sidebar and alerts you when anything happens, helping you to strike at the right moment. Unfortunately, the alerts misbehave on 3.0.1. Update, please!
https://addons.mozilla.org/en-US/firefox/addon/5202

2. Amazon Shopper
Amazon's prices change from day to day, so tell this nifty plug-in what you're willing to pay. When the price drops, it'll let you know.
http://shopaddon.com/

3. RetailMeNot
Discover whether discount codes are available for the site you're visiting. RetailMeNot is a collaborative effort, so the more people that use it the more useful it gets.
https://addons.mozilla.org/en-US/firefox/addon/4980

4. Yapta
Flight finder Yapta includes the main European carriers, although it's best for transatlantic or US travel. The tracking feature lets you know if any flights drop in price.
https://addons.mozilla.org/en-US/firefox/addon/5966

5. Exch
Planning to buy currency? Timing is everything. Exch carries out currency conversions and shows you graphs of the underlying trends.
https://addons.mozilla.org/en-US/firefox/addon/1747

6. CraigZilla
Find bargains on Craigslist from your status bar: select your region and what you're looking for, and CraigZilla fetches and filters the listings accordingly.
https://addons.mozilla.org/en-US/firefox/addon/6288

7. One-Click-Best-Deal
Despite the rubbish name, this is pretty handy: select and right-click on a product name, and One-Click-Best-Deal checks Shopping.com to see if it-can-find-it-cheaper.
http://www.one-click-best-deal.com/