First a primer: a browser is a piece of software that is designed to read a universal language, allowing a website to appear and function basically the same whether you're using a PC, Mac or Linux computer. It allows for two-way communication over the Internet and was the first network protocol that allowed for the simple embedding of images, videos, music and other content.
However, for next-generation rich content like dynamic pages, games, Web 2.0 applications like Google Docs and Splashup, you usually have to download plug-in software like Adobe Flash, Microsoft Silverlight, Sun Java, etc. These days you can also enjoy 3D gaming like Fallen Empire: Legions or Quake: Live, provided you have the right plug-ins and rendering engines (Torque usually, but also Unity 3D) and download a few files to your computer to cut down on load times.
Not all browsers are identical in their ability to run all these plug-ins, which is a problem, and every plug-in has its own limitations. Getting that rich content to work can also be expensive - some programmers hate Flash and consider it obsolete, unwieldy, slow, redundant and hopelessly frustrating. Others have been saying Java is a dead language for years, yet it still appears to be thriving despite its drawbacks. Some programmers even figured out how to use Java to create 3D environments and vector-based graphics.
In an attempt to truly unify the browser experience, developers are hard at work on HTML5 - a next-generation standard that will incorporate a lot of the rich content offered by plug-ins, while also cutting down on redundant code to allow for faster download and data transfer speeds.
The HTML5 revision dates back to 2004 and a conference by the Web Hypertext Application Technology Group. They essentially started over from first principles and in 2008 showed off a working draft of the new protocol. In February they announced that the language is now in "Last Call" testing, and should be released in late 2010 if all goes well, but likely in early 2011.
The new language is cleaner and does away with dated concepts like <font> tags in favour of CSS style sheets that apply general rules to text, tables, inset windows, lists, menus, images and other content to hugely reduce the amount of code required. The result should be a faster, cleaner experience.
There are also new tags for media like music and video, plus built-in graphic interfaces for 2D drawing, support for touch-screen applications, support for offline storage databases, drag and drop functionality and more.
HTML5 could also replace the need for plug-ins in many situations, which will also speed up loading times - although the plug-ins themselves are getting better and designers are working to release versions that will capitalize on HTML5 to crank up the web to another level entirely.