Text size consistancy cross browser / device?

Assuming I make a website's text sizing with em, how much will the sizing 开发者_开发知识库vary cross browser and device? Im actually redesigning a site and if I make the text larger with firebug some of the layouts screw up, how much of an issue is this? Thanks

The most reliable way to keep text size consistent across browsers is to use pixels rather than ems. This defeats older browsers text resizing options, but that's a decision you have to make.