Use Services.obs instead of getService for observer service
Remove unused getService for VersionComparatorService
Remove use of Components.utils.methodjit

It appears that this flag can no longer be set in new-ish Nightlies.
This patch switches code that used nsITimers with the
Components.utils.methodjit hack to use setTimeout on the hidden DOM
window instead, so that we still get the JIT. (See
https://bugzilla.mozilla.org/show_bug.cgi?id=776798)

This might also mean that callbacks from doGet etc. no longer get JITed.
At some point, we should test this with the JIT profiler.