i built the DOM Inspector extension for Sunbird 0.3 and 0.4a1 (nightlies).
You can download it from the german website of Sunbird and Lightning:
Please report back, if you find problems with the extensions or future
I have attached a DOM Inspector build from SUNBIRD_0_5_RELEASE
source code for Sunbird 0.5 in Bug 354083.
PS: Until AMO allows extensions to be added for Sunbird 0.5, my
complementary extension for DOMi, InspectorWidget, can be found at my site: