We developers are a busy bunch, and having almost daily interruptions asking us to update to the latest bleeding edge version is, well, annoying. I know you want us to be current, but this needs to be balanced with letting us get our jobs done too.
How about a setting like "Send update notifications no more than: ", with a number of days, or a week, or a month. Something. I like Firefox DE, but it is getting to be frustrating.