Incoming smug report:

What about a website that contains the majority of the functionality and content, such as houses etc. perhaps even stored online so your cities can be accessed across browsers and PCs etc. and then write page data and other things only extensions can access to the page's Local Storage, so you only need to implement and maintain the tab code in browser extensions, and people could try the app without installing an extension for their browser, or contribute to their cities with browsers that never will support the extension(my phone is very old...)

It seems to pause if you lock your computer, which I quite like because it stops me from being able to pause it and browse reddit. Perhaps this functionality should be more obvious though.