The following asserts are failing when opening Web Inspector:

[Error] Assertion Failed: Object.addEventListener: invalid event type  – undefined – "(listener: " (4)
function (event) { WI._tabBrowserSizeDidChange(); }
"thisObject: "
null
")"
	addEventListener (Object.js:39)
	(anonymous function) (Main.js:280)

[Error] Assertion Failed: Object.addEventListener: invalid event type  – undefined – "(listener: " (4)
function (event) { WI._tabBrowserSizeDidChange(); }
"thisObject: "
null
")"
	addEventListener (Object.js:39)
	(anonymous function) (Main.js:284)