I was just wonder, let's say that there is a question which asks how to disable the cache in Firefox, and the person who asks says that they are running a supported flavour and version of Ubuntu, is this question allowed even though it wouldn't matter which OS they were running, nor which site they posted on (could be Linux, Unix, even Windows)? I mean, if they are running Ubuntu and want to know how to do something with some software, is it on-topic if it is non-Ubuntu-specific? And where is the line drawn because I have seen many of these questions closed, but many left open?
You can —and people have tried to— make the argument that we should only handle things that are "strictly Ubuntu". What is that though? What is Ubuntu specific? Ubuntu is a collection of other people's tools so ultimately, very, very few things are actually specific to Ubuntu.
Sidestep the madness that comes from prescribing a strict "line" around on-topic subjects. It's folly to try. We aim help people install, use and develop on Ubuntu. It's that simple.
Please don't chase questions around with pitchforks because the underlying software also exists on another platform. The same can be said for 99% of the software available in Ubuntu.