This list is by no way comprehensive (or new), but does list a few extensions that I found irreplaceable that you could use with your firefox browser.
The first in the list is Firebug. Written by Joe Hewitt, Firebug has the ability of cutting down your coding time. You’ll no longer find yourself using the Error Console which is inbuilt in Firefox, Firebug relays all the bugs that it can find, even on pages beyond the one you’re looking at (via Ajax). You can customize your firebug to work with only a few sites, you can preview the site and change the CSS on the fly. Of course that’s just scratching the surface.
As a web designer, you must have had issues with certain images or layouts being off by just one pixel. In comes MeasureIt, a tool to measure the height and width of certain segments of the page.
ColorZilla is a cool extension which allows you to check out colors using a color picker, or you can choose from an entire palette.
If you don’t want to use a tool like Webshot to take screenshots of entire pages online, you could use Screengrab! a nifty tool that will allow you to take screenshots of what is currently on your screen - you can even choose the portion of the screen you want to “grab”. This is especially useful if you want to take a shot of a personalized page which requires a log in.
Firefox Web Developer is a favorite for many, many designers and coders I know, I personally don’t use it as much as I should, but do believe that this is a very useful tool in the long run, especially once you get used to it. It adds a toolbar to the top with a ton of features.
The tough parts of web development is the compatability issues developers face with Internet Explorer. IE Tab extension allows developers to switch between IE and Firefox browsers with just one click, especially really helpful with viewing the results of your CSS and javascript codes.
Another aspect of a perfect design is getting your pages validated according W3C standards and Html Validator is the perfect tool for it. This plugin validates your pages within your local system and dosen’t send your pages somewhere for validation. It also upgrades your view of the page source along with and error log and an example on how to fix the error.
CSSViewer is a tiny plugin that instantly displays the current CSS attributes of a html element when you roll over it on the page itself. With its ease of use and the information it displays most of the designers will just fall in love with it once they get used to the plugin.
FireFTP converts your Firefox into a simple and powerful FTP client where you can upload and download your files from remote servers. It also allows you to manage multiple ftp accounts within a single Firefox profile.
译文:
Firefox 9大插件今天你用了吗？
这张列表覆盖面或许并不全面（可能也不是最新的），但是确实列出了一些在使用
firefox浏览器时必不可少的扩展插件。
1. Firebug
首先出场的是
Firebug。Firebug可以缩短编码的时间，以后使用Firefox自带的Console时再也不会出现错误了，因为Firebug修补了所有它能发现的错误，运用Ajax技术甚至可以修补你尚未查看的网页上的错误。你可以设置Firebug仅在特定的一些网站上运用，预览网站后改变动态的CSS，当然这只是小试牛刀。
2. MeasureIt作为一个设计师，可能你碰到过这种情况，仅相差一个像素的图片或布局就无法使用了，现在有了
MeasureIt你可以准确无误的测量网站上任意部分的高度和宽度。
3. ColorZillaColorZilla是一款十分强大的取色器，你可以用颜色选择器或从整套调色板里取色。
4. Screen Grab如果你不想再用Webshot之类的软件来截取网页，试试
Screengrab!吧，这个实用的插件可以把你正在浏览的页面全部截取下来，当然也可以只取一小部分，如果要截取登录后才能查看的页面时，这个工具更是派上了不小的用场。
5. Web Developer据我所知，Firefox 的这个
Web Developer插件是许多设计师的最爱，我个人不太用这个插件，但我还是相信这个工具十分有用，特别是用惯了以后，更是离不开它了。只需在页面顶部加上个工具栏，就有大量功能供你使用了。
6. IE Tab网站设计中最头疼的部分就是IE的兼容问题，有了
IE Tab用户只需轻轻一点就能在IE和Firefox间自由转换，特别是在查看CSS和JAVA脚本运行效果时，这个插件就帮了不少忙。
7. HTML Validator对于一个完美的设计来说，验证网页代码是否符合W3C标准也很重要，
Html Validator就是用来帮助改正HTML语法错误的。这个插件可以让本地系统上的页面生效，而无需把网页送到其他地方去确认。它还能顺便升级你的页面源代码，并教你如何改正错误日志。
8. CSS ViewerCSSViewer 是个小型插件，可以用来查看网页上任意区域的CSS代码，鼠标指到哪儿就显示哪儿的CSS代码，由于使用方便，而且实用，所以深受许多设计师的喜爱。
9. Fire FTPFireFTP 可以把Firefox转换成简单却又功能强大的FTP客户端，这样你就可以从远程服务器上下载和上传文件了，同时还能在一个Firefox文档下管理多个FTP帐号。