Firebug 1.6a16 won't open in last Minefield (4.0b2pre as of today)
update with this message in the error log :
Error: uncaught exception: [Exception... "Component returned failure
code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE)
[nsICategoryManager.addCategoryEntry]" nsresult: "0x80070057
(NS_ERROR_ILLEGAL_VALUE)" location: "JS frame :: chrome://firebug/content/firebug.js
:: anonymous :: line 145" data: no]