Hi
Nothing major, but asking if one of you guys ever had the same thing.
Occasionally (so...random) when I reboot the laptop a file of the following type appears on the desktop
e.g. zNissial.html.part and always of the xxx.html.part type
A residue of something else part of the boot process ?
Properties doesn't show anything worth it except: Empty document (application/x-zerosize)
I send to bin. But then another one will appear again at some point. Never the same name.
W
Interestingly, when I searched for this problem, I found examples of this happening on all OSs. Windows, Apple and Linux (various distros). The common theme seems to be they started to appear after software installation. One that was called out was uTorrent. Others had issues when composing emails in Thunderbird or writing posts in Wordpress.
Here is the search I used on Brave:
If it were me, I would go into the terminal and run update, upgrade and then autoremove. Then I would go through the last couple of peices of software, especially ones I deleted and make sure they are fully installed and/or deleted.
I would also check what programs I have running in the background. Perhaps something is being generated from these programs during the shutdown or startup process.
I am no linux expert, however, but perhaps this will help you get started trying to solve this. Keep us posted.
That is Firefox feature to assign .part extension to partially downloaded files. Why FF tries to download some file without your consent remains a mystery. Some recipes are mentioned in the following pages:
https://support.mozilla.org/en-US/questions/1375411#answer-1511847
Nice! Since I don't use FF it has never happened to me but this is great!
I use firefox & thunderbird a lot, and have never seen it, but I see them all the time on my wife's computer, I assume operator error, see watches a lot of cat videos 
I also use firefox & thunderbird a lot. On a daily basis. For business. So, no furry species (!!) of any kind or else. 
Since TB is now a snap, it creates a file part of the Downloads directory called thunderbird.tmp; where are essentially copied all downloads of attachment to emails. I clean it about twice a week.
Maybe the 'x.html.part' are connected to it. I didn't think about it.
I'll look into the links you guys provided, though.
W