I’ve been using Mozilla Firefox as my main browser since version 3 was released and one of the best things about it is it’s excellent addon capability. Here’s a list of my top 10 favorite addons that I currently use with Firefox:

1. Live HTTP headers

Excellent for debugging of request/responses when developing web pages. This addon allows you to easily inspect all request and response headers so you can easiliy check that you get the content type you’d expect and so on. The only thing I don’t like so much about it is that it captures all HTTP traffic and not just the current tab, so if you have some ajax page, like for instance GMail in some tab the traffic will constantly show up in the Live HTTP header window. You can configure filters to avoid this, but well, that’s just annoying.

2. Adblock Plus

Comes with a whole bunch of preconfigured URL patterns that serve ads and should be ignored. This really makes a huge different when browsing the web and you don’t really appreciate the full value of it until you are forced to browse the web through some other browser that don’t have any ad blocking.

3. Firebug + YSlow

An incredibly useful plugin when debugging javascript pages. This allows you to step through your javascript code, inspect the DOM, modify the stylesheet(s) and see the changes live. It also gives shows you the request and response headers from XHR requests made from the page (similiar to the Live HTTP headers addon but only for XHR requests). YSlow is an addon to Firebug from Yahoo that analyzes the page and gives you tips on optimizing the performance (compressing javascript, serving files from a CDN network etc). I don’t really use it all that often, but it’s a nice to have.

4. Webmail notifier

The webmail notifier addon puts a grey envelope in your Firefox status bar. If you receive mail it can popup a notifier over your systray, regardless of what application is active and the envelope changes to yellow to indicate that you have new mail. It works with Hotmail, Yahoo, GMail and more. Even if you use GMail, get this instead of the dedicated GMail notifier which constantly requires you to re-login.

5. del.icio.us bookmarks

This Firefox addon integrates del.icio.us bookmarks with Firefox bookmarks. So you can keep on bookmarking (CTRL-D) as usual and the bookmarks are saved directly to del.icio.us. It also gives you some neat icons in the Firefox systray that indicate bookmarking activity in your network and such. The best thing about it is the easily accessible sidebar that has a neat incremental search feature so you can easily find bookmarks based on your tags and/or notes.

6. Colozilla color-picker

Need to now the color value of some element or image on a page? You don’t need to save a screenshot, open it up in photoshop and pick the color. With this addon you can simply click on the picker icon in the status bar and click anywhere on the page and you get the hexadecimal color value!

7. User agent switcher

This addon gives you an easy way to spoof the user agent that Firefox sends. Really nice to use when creating custom pages for iPhone and different mobile browsers. Unfortunately the list of user agents that comes with it is very basic (just a few web browsers), but you can easily add or import a text file with more user agents.

8. XHTML Mobile Profile

By default Firefox refuses to show the page when the content type is XHTML Mobile Profile (even though it’s really just XHTML content with a slightly different content type). This addon fixes this and allows to view these pages in Firefox as well. A minor annyoance with the plugin is that it validates the XML and chokes if it doesn’t validate while most mobile phones just carries on and ignores the errors.

9. Google Gears

Gears gives you an embedded SQLite database and a threaded task runner that javascript can use and interact with (if you allow it explicitly). There’s not too many sites that uses it, yet, but Google Reader is one where it works really well for offline browsing of RSS feeds.

10. Google Notebook

This is a nice extension of the Google Notebook application that allows you to access your recent notes directly from the Firefox status bar, and to easily highlight text on web pages and add it directly to the notebook, preserving HTML formatting and links. I use it all the time for quickly making notes about anything from shopping lists to linux command one-liners as well as meeting notes. Since it’s from Google it’s of course easily searchable just like GMail and Google Reader and you can always reorganize, tag and share notes later.

Well, that’s my top 10 list, what are you’re favorite Firefox addons/plugins?

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