Google Global allows you to see what organic and paid Google search results look like as they appear in different countries, cities, regions, ZIP codes and IP addresses. You have the choice to depersonalize your search – I find this useful when I don’t want Australian sites to dominate. A little button with drop down menu and options allows you to easily switch your preferences.
KGen KGen(Keyword Generator) is very useful if you are looking for ideas for your current or planned sites as it allows you to see what keywords are strong on visited web pages for search engines.
Live HTTP Headers allows you to view the content of headers of the page you are visiting. This is useful to check to see such things as what keywords are being used in meta tags and descriptions.
SearchStatus Displays the Google PageRank, Alexa rank, Compete ranking and SEOmoz Linkscape mozRank and incorporates a keyword density analyser, keyword/nofollow highlighting, backward/related links, canonical links, WHOIS, robots and more.
SeoQuake SEO extension A toolbar that helps with search engine optimization(SEO) and promoting your websites with tools such as keyword density checking, the number of internal and external links ands showing Google, Yahoo, Bing and Alexa rankings.
SenSEO SenSEO is an extension checking the most important on-page-SEO-criteria and calculating a grade of how good your site fulfills these criteria.Comes as part of the Yslow add-in.
Clip to OneNote Send text, pictures to Microsoft Office OneNote with a single
easyComment helps you speed up your blog commenting by making it easier to use multiple profiles such as name, email, urls.
Evernote Web Clipper This add-on allows you to save information via a toolbar button and context menus to your Evernote account.
Gmail Manager A "you’ve got mail" pop-up notifier which you can set up with multiple Gmail accounts. along with viewing account details including unread messages, saved drafts, spam messages, labels with new mail, space used, and new mail snippets.
Hyperwords Highlight words on a webpage click a small button that appears and search for them on Amazon, Google, Google Images and Video or Wikipedia; search reference sites Merriam Webster, Google define or Wordnik. Share with the pagelink on Facebook, Twitter or by Email. It even converts currencies and translates.
iMacros for Firefox helps you automate your repetitive tasks such as visiting the same sites every days, filling out forms, and remembering passwords.
Memory Fox reduces the browser’s RAM Memory usage leaving more free for other applications you are using at the same time.
Read It Later is a bookmarking tool for saving pages you particularly want to go back to. You can save to a Read it Later account and access your bookmarks from any computer. It is is one of my favorites because of its wide features and use with other applications and platforms, such as smart phones.
ReminderFox displays and manages lists of reminders and ToDo’s. ReminderFox makes sure you remember all of your important dates via easy-to-use lists, alerts, and alarms, right in your browser without the need for a separate calendar program.
Simple Timer is a clock/timer on your statusbar/toolbar that helps you manage your time
Tab Mix Plus is must have for me which gives options as to how you want your tabs to behave. Great if you have a lot of tabs open at once.
AddThis is a sharing and bookmarking tool to use with a selection of online services.
Shareaholic Share links on Facebook, Twitter, Google Mail, Reader, Bookmarking sites, Evernote, Bitly, StumbleUpon, and more…
Web Design and Image Management
ColorZilla is an Eyedropper, ColorPicker and Page Zooming tool which is very handy if you want to find out what colors are used on websites.
Down ThemAll!A download manager for use within Firefox – download all the links or images contained in a webpage with options to choose what you want.
FireShot- is a screenshot tool that captures whole web pages in image form. You can then annotate and save these or upload to online image sites such as Picasa and Flikr.
Screengrab – Save a selection of a page or the whole page to the clipboard or to a file as an image, including Flash.
Web Developer adds many tools that are useful to see the design and coding of a webpage.
YSlow If your website is running slow this tool will analyse them and let you know where you can improve. You must have the Firebug add-on installed for this to work.