firefox plugin to test web application

Question

is there any firefox plugin to emulate slow internet connection or emulate unstable internet connection to test web app?

Answer 1

I don't know any but if you have a phone with a data plan, you could use it as "internet provider" on you PC in order to simulate the slow connection (Tethering)

Answer 2

Instead of extensions, network tools can be used to simulate different connection behaviours - see e.g. "Network tools that simulate slow network connection" or "Bandwidth throttling software".

Unless for some reasons the APIs exposed by FireFox give extensions control over its networking features, this wouldn't even be doable without external applications.