Firefox only (Windows/Mac/Linux)
This Firefox extension FoxReplace adds find-and-replace functionality to web pages. If you do a lot of writing in web forms—whether it’s for work, your personal blog, or just your Gmail account—the option to do automatic find and replace is a godsend. You can choose to match by case and replace all matching text, whole words only, or use regular expressions if you’re really savvy. The extension boasts way more features than you’re likely to use (including finding and replacing text on an HTML level), though to be honest I’d be happier with a similar extension that worked only with textareas and had a Find Next option before replacing (right now it replaces all instances). FoxReplace is a free download, works wherever Firefox does.