Turns out that the IFAB is composed of the football associations of England, Scotland, Wales and Northern Ireland (who have one vote each) and the FIFA executive (which has 4 votes) who effectively represent the rest of the world! Furthermore, decisions must be approved by 3/4 of those present and entitled to vote. Effectively, this means FIFA plus two UK national football associations.
According to the BBC website, the Football Association of Wales and the Irish Football Association have been siding with the FIFA executive in opposing goal line technology.
The FIFA website does a pretty good job of explaining the history of the IFAB (with some additional details from Wikipedia) - when it was founded in 1886, International meant the four Home Nations and FIFA didn't joint till 1913.
Wow. That's one Hell of an interesting system!