root cause: Eclipse 3.4.1 is not compatible with some versions of xulrunner (will be fixed in Eclipse 3.5)
If the IDE does start up and you select Help->Welcome you get an SWT error. Also some of the buttons, e.g. in the project wizard can not be selected or submitted via mouse pointer.
A workaround is to disable the Welcome page display as follows:# cd YOUR-WORKSPACE-DIR
# rm -rf .metadata
# mkdir -p .metadata/.plugins/org.eclipse.core.runtime/.settings
# echo showIntro=false > .metadata/.plugins/org.eclipse.core.runtime/.settings/org.eclipse.ui.prefs
To permanently allow you to work with the welcome and html-pages, you will need to download and install the gdk_eclipse_fix with the Package Manager.
You may still have some buttons which can be selected with the mouspointer but not submitted by pressing a mouse-key. In that case, the workaround is to press the keyboard "TAB" to navigate and "Enter/Return" to submit those buttons.