When will you fix this bug ?
I want to quickly and easily test pieces of code without going into the online editor !!
I am unable to reproduce this bug. Could you give detailed steps to reproduce what you are seeing? What version of Firefox are you using?
Are you executing the same code block more than once? Of course that will fail as you are declaring a a second time.
Refresh the page you are debugging and you can execute the commands again. And if you leave the development tools window open you can even press Up-Arrow to get (and edit) the previous commands after the refresh.
I think this is tracked in https://bugzilla.mozilla.org/show_bug.cgi?id=1257088
another workaround is to wrap the expression in a code block (if you don’t need to access the variables after):
{
let a;
let b;
a = 23;
}