Each browser reads your webpage differently. Firefox does not read a site as internet explorer or opera or chrome. Each browser has it’s own specifications. So, you need to build up a site for all browsers. I mean, your site can be accessed from all browsers and they all should reflect the same thing. But how to know that?
I am listing few websites below which will read your sites and will show you the result. They can tell you that how is your site being read by firefox (most used browser), IE (very less effective, though MS people made it), Opera (just ok), Safari (under estimated) or chrome (need improvement). It will also guide you with your source code, if you have any.
1. WEBXACT
Webxact shows your web site’s load time,total bytes of your web site and broken links on your site,but the problem is webxact scans very slowly,instead of webxact you can use pingdom to see your website’s detailed information.See my blog’s information from pingdom.

2. CleanCSS
Clean Css scan your web site’s css and converts long codes to shorter ones such as 0px to 0,#FFFFFF to #FFF and it shows errors in CSS.After fast scanning my CSS became like this : Input: 73.617KB, Output: 66.708KB, Compression Ratio: 9.4% (-6909 Bytes)
Its a famous css validator which shows your web sites css errors.
Review your website on different mobile phones like nokia,motorola,sony ericson,sharp,see load time of your website when connected via Wifi,3G and GPRS,it will also show the cost of loading your web site.
5. TAW3
This tool downloads your website and it shows you tips about what should you do to make your web site better.
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