Thank you so much !!!
The first version (created originally by Allice0775) was a must-have , and after its wiping from here there wasn't a similar addon.
I haven't yet believed I shall encounter such a good addon like the original one.
This is almost so good as that was.
Of course it needs some polishing, but it seems (by the number of versions made in the last two month period) that it is under heavy developing, and it is much more than okay. :-)
I'm so thankful for this addon and the efforts behind it.
A fantastic and great job in the new world of Quantum's webextensions. ;-)

On the other hand, it can be used in Faterfox (which is based on Firefox 56).
I use it in both browsers with satisfaction.
Thanks again.

Best regards,
Gammadeus

P.S.
If you could make the remake of Allice0775' s other great and highly rated addon, the "Default Full Zoom Level", there would simply be the heaven.
With separeted icons (the red "P" and the blue "A"icons for zooming in and out, and resizing the magnification of the page and the size of the letters) there was the best zooming addon for the good ol' Firefox.
Of course it is only a beautiful dream.... But the dreams sometimes come true. . .
And I'm -- as so many others -- an incorrigible dreamer. . . ;-)

......................................................................................................................................................

UPDATE _ 01.

Thanks for the tips, I know both of them. (The Ctrl+mous-wheeling is well known, but it has its own limits.)
Zomm Page WE is good enough (and better than the Mozilla's solution built in Firefox), bot not so good as Alice0775's addon, which one is more simple, and the separated icons (for separated zooming: one for the page zooming and another one for text zooming), with customizable zooming-scale.
If you are interesting in the Default Full Zoom Level addon, I have the original installer file of it (xpi, version 7.7). I collected from my saved old Firefox-56 's directory, so if you give me privat acces / address, I can send for you.
It would be so great to see it again, as a webextension addon here on AMO.
If I knew the proper programming language and I knew coding, I would wright it from the scrach (as a functional fork of Default Full Zoom Level).

Hi,.
Gammadeus

34/5000
Finally! thanks thanks thanks!

This is the first time I've ever rated an extension, and I'm soooo grateful you've developed it! I was so missing the old "Go Parent Folder" and "Show Parent Folder" add-ons. If you save bookmarks in a complex tree, this extension so deserves your attention! It allows you to see your entire bookmarks tree in the same window as the page you're wanting to bookmark, and search the tree for specific words. When searching, it shows you all the folders and bookmarks containing that combination of words. Clicking on a given folder or bookmark in the resulting search list causes the tree (separately displayed) to open up to the place in the tree hierarchy it exists. Right-click (context menu) on an item in the tree, and you can manipulate the folder or bookmark (cut, copy, delete, etc.). Fantastic!

Dev, you are a life-saver !
The Go_Parent_Folder was the main reason why I still was using Firefox ESR.
Now a working Scrapbook and everything back to normal at last.

Maybe a silly question, but why didn't Mozilla add this essential functionality in their FF?

Well, this add-on is quite good and works exactly how I need, but I am missing very much another another one Alice had, which saved me so much time ans nerves. I am talking about the Go Parent Folder in FF library. Maybe you could are it work with the present versions of FF, please? Give us an idea. I tried to tell her this through her site, but it is very difficult and is all written in Japanese and you know Google does not translate many things in there.

@ooFn.
Thank you for your reply. I know about the changes with FF extensions. The information about it was published about one year before it happened. What I meant was a suggestion to adapt alice0075's Go to Parent Folder like you did with this one. I still have the xpi file, now useless, of course.

Very nice work, many thanks.

Favicons are retrieved even when the user has set Firefox to block favicons everywhere:

// disable favicons in shortcuts
user_pref("browser.shell.shortcutFavicons", false);

// disable favicons in tabs and new bookmarks
user_pref("browser.chrome.site_icons", false);
user_pref("browser.chrome.favicons", false);

// disable favicons in web notifications
user_pref("alerts.showFavicons", false);

Having 'Bookmark search plus 2' respect Firefox's favicons' settings would be appreciated.

EDIT after developer's response :

Since it is not possible to synchronize the favicons' display with that of Firefox maybe an option specific yo BSP2 regarding Favicons would do it, as for instance in the 'Flagfox' extension, such as 'Favicons Yes/No'
This is neither an issue nor even a true enhancement, but an option for users who wish not to retrieve Website icons (which by the way also adds time to the process). I think more users than we may imagine block favicons.
The idea is that I don't see why connections to sites would be performed for accomplishing a task (localizing a bookmark in the Library) which is basically an off-line process.

EDIT 2 :
Version 2.0.15 now includes a 'Disable favicon fetching' option : rating updated from 4 to 5 starts.

Had not idea about drag-n-drop (1). You have to publish these reviews as separate book(mark:). Thanks a lot for addon.

Finally an extension that shows parent folder. Good job!

For some reason, after performing a search, the results keep flashing as though it keeps refreshing. That's a problem because when I try to scroll down the results list, it refreshes after 1-2 seconds and sends me back to the top. I don't see an option to turn off this constant refreshing.

I'm sure the developer will fix this, so I'll still give it 5 stars. I'm happy to have the parent folder search.
Thank you!

First extension since Firefox 57 to include the "go to parent folder" functionality. Great!

At last I can find my bookmarks in my folder structure. Thanks a lot.