Firefox "non-standard"  keyCodes for +- ...

I noticed that Firefox* uses different values for event.which and event.keyCode when pressing the +/= (61) and - (173) keys near backspace. 

I have no idea why firefox is different, but it is, and since e.which and e.keyCode are not part of any W3 or WHATWG specification they aren't necessarily in error by being different, its just something that needs to be accommodated.  

* Safari/Chrome/IE are all consistent, FF is the odd one out. The Windows key and semicolon key are also different keycodes in Firefox, but I didn't put those modifications in....