Add HTML5 "desktop notifications" on Firefox.

Doesn't quite work on Chrome and I haven't checked Safari yet.
Desktop notifications fully functional on Chrome.

Might be broken on Firefox now though.
Notifications working in Firefox; haven't tested case where blocked by browser.
Fixed Firefox notification handling when blocked by browser
Added alert indication Notifications aren't implemented on Safari (untested)
Merge pull request #122 from aiannacc/html5-notifications

Html5 notifications