The hard part of doing Find in a browser-based app is figuring out how to reliably get the keystrokes for Find and Find again, Cmd-F and G respectively.
The browser has its own Find, but an outliner like Fargo really needs to do it for itself. The browser doesn't know about text that's tucked away under collapsed headlines, for example. And it shouldn't be searching the menus and the text in the right margin.
It works well in Chrome and Safari, problems in Firefox.
This is something the browser guys should get together on, imho, if there's going to be a browser-based apps ecosystem.