Why does Firefox store all my visited domains, even when I'm using
"never remember history" and clear all cache, use bleachbit to clear
Question: Is this a privacy issue? Why does Firefox do such a thing?
Only you can decide if this is a privacy issue. As long as noone can read the files in your profile, probably not. Otherwise it might be.
Firefox itself should not do this if you set "never remember history". However, an addon may do this on its own.
How to find out which add-on causes this?
You can look at the name of the file to find out.
The filename you give is:
The part after "jetpack" ("aaa1-aaaaaaaaaaaaaa@jetpack" in your example) is the ID of the add-on responsible for this directory. You can look up this ID in
addons.json in your profile folder.
If the ID is not in
addons.json, the add-on is (no longer) installed - in that case the files may be left over from a deinstalled add-on. In that case there's probably nothing to worry about, because the file will no longer be updated. You can probably delete it (keep a backup though, just in case).
If you still want to know what deinstalled add-on was at fault, you can search for the add-on ID on the web. This will usually tell you what add-on uses this ID.