Droimeanna

Droimeanna turns any page with Irish into seanchló.
This means that instead of consonants-plus-h you have
consonants-with-a-dot-over-them.
ḃḂċĊḋḊḟḞġĠṁṀṗṖṡṠṫṪ

It works on Firefox, Chrome, and Safari.

Currently it uses presence of the word "a-g-u-s" to detect a page with Irish.

Droimeanna as a Firefox Extension (.xpi)

Install Droimeanna

Droimeanna as a Google Chrome Extension (.crx)

Install Droimeanna

Droimeanna as a Safari Extension (.safariextz)

Install Droimeanna

Droimeanna for Greasemonkey

Greasemonkey is available on Firefox and other browsers.
Get Greasemonkey if you don't have it already.
Install Droimeanna for Greasemonkey

Droimeanna as a bookmarklet

You can copy this link which is just javascript,
and then paste it into the address field of any bookmark you like:

bookmarklet

Méarchlár Seanchló do Fhuinneoga

Download Seanchló Keyboard
The apostrophe key (') works as a dead-key, just like with US-International keyboard.
The deadkey with the vowels makes the fada accent over the vowel.
When used with consonants, the deadkey will make a dot over the consonant.
You can also get the alternate lower-case r and s by pressing alt-graphics (the right alt key)
at the same time that you press r or s.
It even works with the deadkey to produce alt lower case s with dot.