Say you boot into Linux from a brand new Live USB. The USB is write protected. The memory stick has never been exposed to the Web in its life. You surf all day on Firefox building your library of bookmarks. You backup your bookmarks to a .json file and send it to your Gmail account. You close down the computer and erase ram. Nothing is saved to the stick.
Five minutes later you cold boot into Linux with your USB still in write protect mode, open Firefox, go online to Gmail and download the bookmarks file. The moment the file has finished downloading you go offline. You restore the .json file to Firefox then set your USB to write mode. You save the new configuration to the USB, close down and remove your memory stick.
What are the chances this stick is now infected with malware, keyloggers et al using this routine? Is there a better way to keep the USB uninfected?