Replace text with predefined value in browser

Solution 1:

I believe you are looking for TextExpander.

From their site:

Type more with less effort! TextExpander saves your fingers and your keyboard, expanding custom keyboard shortcuts into frequently-used text and pictures...

Solution 2:

You can do this by setting each replacement word with it's value under System Preferences / Language & Text.

If after trying it out, it doesn't work, you may need to enable the text substitution feature. To do so just go Edit / Substitution / Text Replacement or right click on a editable field for the edition menu to show up:

You could, though, enable the text substitution feature on every Application which supports it just by executing this command on Terminal: defaults write -g WebAutomaticTextReplacementEnabled -bool true