When developing a new website or posting a redesign, it is a good idea to test your website with different web browsers.
Some of the html tags render differently in Internet Explorer, Firefox, Chrome and Safari. Also, if your videos are only available in Flash format, they will not play on computers and mobile devices that lack Flash such as the iPhone and iPad.
The website Browsershots can test your website with different screen sizes and web browsers. Browsershots takes a screenshot from each browser you select so that you can compare them.
For testing mobile sites on a desktop computer or notebook, you can install an emulator program to test your site.
Six Revisions has compiled a list of tools for testing mobile sites and recommends using iPhoney and iPad Peek for testing sites on Apple's devices.
The W3C Markup Validation Service is another excellent resource for testing your webpages. If there is an error in the code of your web page, the validator will reveal the error in its report.