Why Developers Should Suport non-Internet Explorer Browsers (right from the start)
It's a really stupid idea to not support non-IE browsers because one unhappy person counters ten happy people.
Also early adopters who blog mostly use Firefox (or Safari, Opera or Camino). So in the phase where a project needs attention and free marketing, IE users account for less than 50% of pageviews (probably).
Also, if you're deprioritizing my preferred browser now, why should I believe you'll do any different later on? You're setting a precedent - indicating your approach and philosophy and this is what I'm buying into.