This extension has served me well. I thank its creator.

does the job!

Contrary to the original Keepass Helper addon, when we drag and drop the url to Windows Explorer, it does contain the additional hostname in it... This may be not wanted (I have to rename the url link file in Windows Explorer each time).
Also, the hostname does only appear in the title bar when the tab finish loading. For long loading tab, this can be an issue, we have to wait. Could you add the hostname at the beginning of the tab load, not at the end?

Even though as delivered Firefox 56 (Nightly) does not display a Window Title (can be added through the Firefox Customize screen), it is still present and other programs can "see" it, whether it is displayed or not, and some programs, including the password manager KeePass, look at that title for matching the screen to the appropriate logon credentials. By having the host name in the Windows title, I can use the host name in KeePass as the unique identifier so, in many cases, logon just becomes hitting a hotkey. (Without this extension, I have to do a search on the KeePass database for the server before I can use a hotkey to paste in the credentials.)

This particular extension is in WebExtensions, so it should survive the Firefox 57 transition.

I have been using extensions like this one for years with KeePass and I have never had any issues with them, but I am thankful that there is an extension, this one, that is already written to use WebExtensions and thereby survive into Firefox 57!

If all you need is a host name in the Windows title for the tab that is in focus, this is GREAT! :)