There are many programs and tools that a designer can use to create and implement a design. A browser is one of those programs.
As for the relevance of that to Graphic Design, we should be allowing the same types of questions that we would if they were using any other software. That means that so long as the question deals with design and is clear, focused, can be answered with something other than opinion, then it should stay.
Based on some of the questions that are currently on GD like Need to replicate a split toning (with a colored image), How to create a 3D layer explosion/expansion in Photoshop?, and Slanted text with background box, they don't even need to show code (please correct me if I'm mistaken here), they just need to deal with design. This means that questions asking "what library is this used", "why isn't this code working", or something similar are off topic.
If the OPs in the questions above were to specify they want to use CSS instead of Photoshop or Illustrator, why not allow them?
In summary, if the question can be thought of in general terms as a design problem and is a good question then it should be allowed, regardless of the tool that the OP is using.