Let's say my Firefox extension has multiple preferences, but some of them are grouped, like check interval, fail retry interval, destination url. Those are used in just single function.

When I subscribe to preference service and add observer, the observe callback will be called for each changed preference, so if by chance user changed all of the settings in group, then I will have to do the same routine for the same subsystem as many times as I have items in that preferences group. It's a great redundancy!

What I want is observe to be called just once for group of preferences. Say

extensions.myextension.interval1
extensions.myextension.site
extensions.myextension.retry

so if one or all of those preferences are changed, I receive only 1 notification about it. In other words, no matter how many preferences changed in branch, I want the observe callback to called once.