This script adds an IPA keyboard button to the editing toolbar
If you use Noscript, this bookmarklet is the way to go.
If you click the little schwa button on the editor, a keyboard will pop up. You can use it like any normal on-screen keyboard, just click on the symbols.
The blue circled letters are so that one can easily find a symbol1 (they look similar to the symbols in their group). They also double up as keyboard shortcut indicators. For example, if you press and hold Alt, hit A twice, and release Alt, you get the second symbol in the "A" group, that is, the a-e ligature. This lets you cycle between symbols rapidly, without even having to look at the keyboard. For example, a typical procedure would be to identify which letter the symbol looks like (pretty easy), hit Alt, keep pressing that letter until the symbol shows up, then release Alt. If you can't find it, they keyboard is right there.
1. Idea taken from http://ipa.typeit.org/full/