As a rule, for ever Linux based desktop that I've run (work, home, over 15 years.. maybe 50 unique installs/upgrades that lasted), the most most consistently flaky glue has been Java working in any browser.
Historically, I stumble across, and need, Java applets pretty infrequently. As a result, nearly 100% of the time I do stumble across, and want to run, a Java applet, it involves somewhere between 5 and 30 minutes of fucking around to make it work. Netscape, Mozilla, now Firefox automatic plugin find/install has worked exactly 0 times for a JVM. And, except for the last year or so, it was always a regular fight at java.sun.com to figure out exactly WTF I needed. I consider myself an educated person, but my paths usually led me to download a 200MB blob that included a IDE, but not a plugin for my always up to date browser. And does installing the JRE actually install the pulgin, when I do manage to get the right thing? No. Creating symlinks is apparently beyond Suns ability. Or maybe its a Java security thing; its quite willing to take up 2GB of memory, but creating a symlink is a violation of security. Fuckers.
In the last 18 months, I spent 9 of them as a Java developer, on a team of 13. I've yet to hear an adequate explanation as to what the difference between JSE, JEE, Java FX, J2ME, JDK, in less then 500 words. Sure, I know it now. Well, maybe not. WTF is JavaFX, and why, just now, when I click on "download JEE", it asks me to download "Glassfish"? THAT ISN'T WHAT I FUCKING ASKED FOR.
It amazes me that people are willing to put up with this shit at all. For a language that isn't even that good.
Anyway. If Sun has finally managed to ship something that actually manages to install a plugin without me digging around on the command line, I'm amazed. That it installs an extension as well is a small price to play.