If you're wondering why Eclipse keeps on crashing when rendering an autocompletion pop-up then see the following bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=522635
The workaround for now is to use the XULRunner 1.9.2 shipped with Ubuntu rather than the older version shipped with Eclipse. Do this by using the following:
eclipse -vmargs -Dorg.eclipse.swt.browser.XULRunnerPath=/usr/bin/xulrunner
There's also a workaround involving setting GRE_HOME to a nonsense path, e.g. /tmp.