Another plugin I have made ready for NetBeans IDE 8.1 is the Maven Hierarchical View:

http://plugins.netbeans.org/plugin/45180

It is also available on GitHub:

https://github.com/GeertjanWielenga/MavenHierarchicalView

It's been verified by the NetBeans community and if you go to Tools | Plugins, look for "MavenHierarchicalView", and you'll be able to install it directly into NetBeans IDE 8.1.

When you've installed it, you'll be able to browse into modules within modules and you won't need to open projects separately, for browsing purposes:

The above project comes from here: https://github.com/jamesward/maven-multi-module-example and can be checked out via Git support in NetBeans and without doing anything at all, no configuration, it simply works in NetBeans IDE.

Note: The plugin is really quite simple, take a look at the GitHub repo linked above. It does what it does, it works for its purpose, specifically if you're browsing through your code and you don't want to have multiple different projects open at the same time.