I guess the web related software questions can be asked in either of the websites - superuser or webapps? Am I correct?
If it's about a problem with the browser, it belongs on Super User.
If you have an issue with using a website or web app, it belongs on Web Apps.
However, if you have a question about browser plugins that interact with specific web apps, I I would encourage anyone to ask these questions on Web Apps, rather than Super User
All website related questions are explicitly off-topic for Super User, as you can read in our FAQ
Refering to the FAQ:
Super User is for computer enthusiasts and power users. If you have a question about …
computer hardware computer software and it is not about …
videogames or consoles websites or web services like Facebook, Twitter, and WordPress electronic devices, media players, cell phones or smart phones, except insofar as they interface with your computer a shopping or buying recommendation … then you're in the right place to ask your question!
and the FAQ of Web Apps states:
What kind of questions can I ask here?
Web Apps - Stack Exchange is for expert and advanced users of web applications, so if your question generally covers …
Gmail Facebook Twitter Google … or any other website which behaves like an application, then you're in the right place >to ask your question!
With that said, it appears that interpretation allows for questions to be synonymous nature.