When SpiderMonkey tried to implement an early error for cases like this:

   alert(08)

as the current spec draft requires, we got bug reports about web sites 
being broken as a result.  Specifically, there were two issues we 
discovered:

1)  Things like new Date(2013,08,12);

2)  Servers sending things like account numbers as numeric literals, 
complete with leading zeros [yes, I know, this is so broken, they're 
still doing it].

I believe we'll be backing out this change; it doesn't seen to be worth 
the web compat hit.

-Boris

When SpiderMonkey tried to implement an early error for cases like this:

    alert(08)

as the current spec draft requires, we got bug reports about web sites 
being broken as a result.  Specifically, there were two issues we 
discovered:

1.  Things like `new Date(2013,08,12);`

2.  Servers sending things like account numbers as numeric literals, 
complete with leading zeros [yes, I know, this is so broken, they're 
still doing it].

I believe we'll be backing out this change; it doesn't seen to be worth 
the web compat hit.