You're using a portable version of TB? All I can tell you is that I've done that routinely, just by clicking Help>about and clicking the update button. All my experiences with portable versions have gone flawlessly. BUT, you're asking for a 'clean install', so I'm unsure of your intent. If the issue is that you have a portable version and want to install a new one elsewhere, the easiest way is to do the install and follow the email setup to allow a profile to be created. Then, exit TB and, in file explorer, locate the profile. It may be named 'thunderbird' in a DATA folder. Poke around until you find it. Then, take the profile from the other portable version, copy into same folder as the profile folder is in. Then delete the initial profile and rename yours to the same name. That does it.