Linux, Chrome or other operating systems excluding Windows, do not have Retina display support in Parallels Virtual Machine. In addition, some third-party software in Windows might not have Retina (high DPI) support, even though Windows OS itself does (Windows 8.1).
Parallels Desktop provides Retina support only for Windows virtual machines, Linux, Chrome and other OSes are not supported yet. Some third-party software for Windows might not have such DPI (resolution) support and look blurry inside the virtual machine. This is not Parallels-related issue and fix can be issued only by this third-party software development.