Ok, I'll probably not have time to better edit this.

• building xpcom components on windows - I managed to get it to work, the trick was to link against xpcomglue_s.lib and xpcom.lib. For some reason, xpcomglue.lib is not intended for components, but for embbeding - didn't understand why the name confusion, but thanks to Darin Fisher for helping on mozilla.xpcom newsgroup.
• I still have to get things to build on macos.
• the java/xpcom component does actually works great ( for the minimal hello world at least), I was expecting some problems or at least a crash or two - I'm a bit scared of seeing everything just work.
  
• probably need to post something ( or find a link ) about the varios ways to use mozilla with java. The conclusion I reached - blackwood is more or less dead wood, SWT is surprisingly the best way to interface from java to mozilla ( even if nobody is advertising the hidden gems ) !
• thunderbird - it seems the javascript thread is also the main thread ( unlike mozilla or firefox where js runs in a separate thread ). So everything _has_ to be async. One more reason using java with mozilla is good.
• I still need to sort out the things in jk2 I want to move on. In a way, this mozilla java plugin is triggered by the death of jk2 - and the goal and means are based on what was tried in jk2. For now performance is not my biggest concern, but getting things to work - so most of the tricks in jk2/tomcat will have to wait.