Sometimes it is laziness on the part of the developer (i.e. only using webkit- prefixes on the new JS/CSS features, even though the moz- prefixed equivalent wor

Sometimes it is laziness on the part of the developer (i.e. only using webkit- prefixes on the new JS/CSS features, even though the moz- prefixed equivalent works perfectly), other times it just hasn't been implemented in FF yet (although sometimes the demos do work in the aurora/nightly versions).