Is it possible to access Components.classes from within a web worker?

If I use a standard thread I'm able to access it just fine, however
when inside a worker, it's undefined. I know a worker supports
importScript, is there a way to import the classes I need?

For example this fails inside a web worker:
var file = Components.classes["@mozilla.org/file/local;
1"].createInstance(Components.interfaces.nsILocalFile );

The reason I'm trying to use a web worker instead of a normal thread
is that it seems using setTimeout within a thread crashes Firefox.