Managing search engine ranking is much easier with the right browser extensions. There are many search engine optimization plugins available for a variety of browsers, putting free SEO tools right at your fingertips.
Here is a list of SEO browser extensions. There are popular SEO toolbars that pull in a cross-section of metrics. Also there are extensions for specific tasks, such as measuring page speed or identifying keywords. All of these plugins are free.

SEO Browser Extensions

MozBar. Access MozBar from SEOmoz for important SEO metrics at a glance as you surf. Easily highlight internal and external links, keywords, and more. Compare link metrics for Google, Yahoo! and Bing with search-engine-results-page overlay. Available for Chrome and Firefox.

SEO Quake. The SEO Quake extension obtains information on any site on the fly. It consists of three functional parts: SeoToolbar (requested parameters are shown in a separate toolbar in the browser), Seobar (requested parameters are shown in a separate, fully customizable toolbar with CSS, HTML block) and output of requested parameters on search engine result pages. Available for Chrome and Firefox, as well as beta versions for Opera and Safari.

SiteTrail. This extension provides site rank, site value, server location, site traffic, SEO statistics, site analytics, and more. Simply visit a website, right click anywhere on the site, and select “SiteTrail” to generate stats. Available for Firefox, Chrome, and Internet Explorer.

Meta SEO Inspector. Use Meta SEO Inspector to check the meta data found inside web pages: HTML meta tags, XFN tags, microformats, canonical attribute, and no-follow links. Available for Chrome.

Check My Links. Check My Links quickly finds all the links on a web page, and checks each one for you. It highlights which are valid and which are broken. Available for Chrome.

SEO For Chrome. This popular SEO extension for Chrome provides easy access to SEO tools. Get Google PageRank changes, backlinks checks, keyword research, social media share improvement, and more. Available for Chrome.

SEO SERP Workbench. This tool allows you to quickly check the position of multiple sites — yours and your competitors — given a keyword. Available for Chrome.

Firebug. This extension helps you monitor CSS, HTML, and JavaScript live in any web page. It can even help you see how long pages take to load and find what may be causing the slow loading times. Check your competitor’s code, and locate the tweaks and tags to boost your rankings. Available for Firefox.

Sorezki SEO Plus. This extension upgrades Google Webmaster Tools, Yahoo! search engine, and Google Analytics with social activity statistics, on-page results, social media information, geo-location search tools, PageRank and search engine ranking. Available for Chrome.

SEO Site Tools. SEO Site Tools displays key SEO metrics in six sections: external page data, page elements, social media, page terms and tools, domain information, and suggestions for your site. Available for Chrome.

Page Speed Insights. PageSpeed Insights analyzes the performance of your web pages and provides suggestions on how to make them faster. Available for Chrome and Firefox.

SearchStatus. Display the Google PageRank, Alexa popularity rank, Compete ranking, SEOmoz Linkscape mozRank, Alexa related links and backward links from Google, Yahoo! and MSN. View the link importance of a site, as well as its traffic importance. Available for Firefox.

SEO Book Toolbar. The SEO Toolbar pulls in many useful marketing data points to make it easy get a holistic view of the competitive landscape of a market directly in the search results. Get links to the data sources so you can dig deeper. Compare up to five sites to analyze the competition. Available for Firefox.

YSlow. YSlow analyzes web pages and identifies why they're slow based on Yahoo!'s rules for high performance web sites. Available for Chrome, Firefox, Opera, Safari.

Rank Checker. Rank Checker allows you to easily check your website rankings in Google, Microsoft's Bing, and Yahoo! search. Available for Firefox.

Ghostery. Ghostery is your window into the invisible web: tags, web bugs, pixels and beacons that are included on web pages in order to get an idea of your online behavior. Ghostery tracks over 1,000 items and gives you a roll-call of the ad networks, behavioral data providers, web publishers, and other companies interested in your activity. Available for Chrome, Firefox, Opera, Safari, Internet Explorer.

SEO for Firefox. SEO for Firefox pulls useful market research data right into Google's and Yahoo!'s search results, including Google PageRank, domain age, number of links to the site, and Whois data. Available for Firefox.

Wappalyzer. Wappalyzer is a browser extension that shows you what websites are built with. It detects content management systems, web shops, web servers, JavaScript frameworks, analytics tools, and more. Get the information you need to plan your SEO strategy. Available for Chrome and Firefox.

Foxy SEO Tool. Foxy SEO Tool is a free, open source toolbar that provides quick and easy access to a multitude of search engine functions, such as Google Site, Yahoo! Site Explorer, Live Fromlinks. Also included are web traffic analysis sites such as Alexa, Compete, Quantcast, popular statistic aggregators like Quarkbase and WebSiteOutlook, and keyword research services. Available on Firefox.

KGen. KGen (Keyword Generator) allows you to see what keywords are strong on visited webpages for search engines. It gives you stats on the content of the page, allowing you to improve your content quality. KGen is also a good tool to view the keyword strategy of your competitors. Available for Firefox.

searchStatus. Display the Google PageRank, Alexa rank, Compete ranking, and SEOmoz Linkscape mozRank anywhere in your browser, along with fast keyword density analyzer, keyword/nofollow highlighting, backlinks, Alexa info, and other SEO tools. Available for Firefox.

Smart PageRank. Smart PageRank is a small, simple extension that gives you quick access to Alexa Rank, Google PageRank, backlinks, and estimated value of the page that you are viewing. Available for Firefox.

SEOpen. Provides quick access to some web-based tools to help with search engine optimization. Quickly check inbound links, PageRank, http headers, and more. Right-click on an open area of a web page, or use the included toolbar. Available for Firefox.

yExplore. This extension provides quick access to search engine and social media information, including backlinks, nofollow links, PostRank social engagement, Compete information, and Whois information. Just right click, select yExplore and then one of the shortcut links to access information about the site you are viewing. Available for Firefox.

 Source: http://www.practicalecommerce.com/articles/3778-24-SEO-Browser-Extensions