Firebug confuses "var" and "let" variables in watch expressions

[joebloe]

I haven't figured out exactly what circumstances cause this, but it
seems that in many cases like:

var x;
function foo() {
//...
let x = 'something';
some_function(); //... ** here **

when Firebug is used to inspect the variables at the starred line, it
thinks that x is the global x and not the let x.

Is this a bug? Is there a workaround, aside from using different names
for let variables?

[John J Barton]

There are several bug reports about issue of local variables, maybe
they are related?