IE was just a nice feature to have available. If you happen to need a web browser control, there's one built in for you right there on every copy of windows. You could get in touch with Netscape and figure out what's required to redistribute their runtime, or just make the call to load up the ActiveX control. whichever is easier for you, dear developer.
Notifications will work great on chrome, and non-chrome clients will kinda degrade gracefully by throwing a javascript error. It's fine. it's just there if you decide you need it, no gun to your head.