http requests get sent twice when Firebug is open

[senr...@ultra.me]

osx 10.9.5

Firefox 39.0

Firebug 2.0.11

While working on a recent project, I started noticing some strange behavior. Certain actions were happening twice, getting logged twice, etc., despite knowing that I only performed them once. I primarily develop on Firefox, and always have an eye on my Firebug network console. My site performs a lot of ajax calls. While testing, the network console never reveals that an API was called twice in a row. However, the end result in my system was that it was called twice.

I assumed something was wrong with my code, or that 2 calls were being made immediately (user or UI implementation error), and that because of the immediate chaining of calls, Firebug was only displaying one of them. This is not the case, sadly. Testing in other browsers, I do not have the problem. Testing with Firebug closed, I do not have the issue.

Fortunately, most end users do not have firebug open, and in my particular case, the impact of this happening in production would be limited. Still, this is bad. Can anyone else reproduce this? Remember, the network console will show no proof. You would need to verify the multiple API calls from API server. It's as if the 2nd call happens, but the browser has no awareness of it.