WebGl is supported in the current beta versions of Chrome and Firefox. Most people who want to get started using webgl can. learningwebgl.com has a step by step process.
Chrome’s beta version installs in a sub directory and does not change or use your current non beta version of chrome. Firefox or minefield from the nightly builds does; although it is not impossible to setup a portable installation in a sub directory or usb stick; But, doing so requires additional steps.
Webgl uses opengl 2.0 which is not the newest version – it is supported by the vast majority of systems. Almost any system which is used for video games has opengl 2.0 or better.
The computers that do not are the ones based on a Intel video driver. ATI does have updates for all of their cards but! But many older laptops use a OEM driver and ATI chipset – those people need to turn to the laptop maker for driver updates.
For firefox there is an alternative to opengl 2.0 installed. The alternative is a software rendering using OSMESA32.DLL.
Software rendering allows webgl to work. However you do not get the same performance increase that comes from a direct interface with the graphics processor unit on the video card.