WebWorker calculates slow regexp matches significantly slower (3x) – firefox only

function processRegexUnique(regex, string, result, done, interval) {
var matchList = arguments[5]||[];
… same as before …
while ((m = regex.exec(string))) {
… same as before …
if (matchList.indexOf(path)==-1) {
result(path);
matchList.push(path);
}
if (interval>=0) {
processRegex.working = setTimeout(processRegex, interval,
regex, string, result,
done, interval, matchList);
… same as before …
}
}
… same as before …
}