As far as the View Pocket List is concerned, while in the Customize for the toolbars move the Pocket button from either the toolbar or the Menu panel into the Additional Tools and Features palette, then close Customize. That will hide the View Pocket List menu item.

Recent Tags can be removed via the right-click (contextual) menu; select the Delete item.

AFAIK, "Subscribe to this Page", "Bookmarks Toolbar", & "Other Bookmarks" don't have a Delete menu item available; they are greyed-out in my installation, but can be hidden using the Menu Wizard extension. That is what I use for hiding menu items that I don't use and don't want to see most of the time, but I do hide items like "Sign in to Sync" and "Remove All" for signins that are in menu areas that Menu Wizard doesn't deal with via my userChrome.css file. https://addons.mozilla.org/en-US/firefox/addon/s3menu-wizard/

Those can also be hidden using a userChrome.css file; IOW, you don't "need" that extension but it makes the "hiding" a lot easier. http://kb.mozillazine.org/UserChrome.css Problem is coming up with the correct code for each menu item that you want to hide. The Developer Tools that are built into Firefox can be used to view the code for anything in the UI. https://developer.mozilla.org/en-US/docs/Tools

Then as far as restoring the default, either disable Menu Wizard or remove the userChrome.css from your Profile; or disable the Stylish extension if that is what you choose to use.

I never got the hang of using those Developer features, so I can't help you with figuring out how it works. But I can steer you towards the User Styles website where Firefox users share their "Styles" which use userChrome.css and userContent.css in the Stylish extension. https://userstyles.org/ Browse the Styles a bit to see if you can find a pre-made Style for those menu items. And once you have the Stylish extension installed you will be able to view the code for every Style posted there. I routinely 'grab' a line of code that I want and put it in my userChrome,css file or use it to create a new Style for myself. https://addons.mozilla.org/en-US/firefox/addon/stylish/

Further information about using Stylish. https://userstyles.org/help/stylish_firefox And there is a support forum over here, where you might get some help with figuring out the code that you need. https://forum.userstyles.org/

Thank you very much! I installed the Menu Wizzard and configured my Bookmarks Menu in two minutes! Fantastic!

@RonRoberts :

You marked your own post as   'Chosen Solution',   -   would you be a dear and mark the-edmeister's post as such instead   ? Thank you   !

Sorry about that! You know how us newbies are.

RonRoberts said

Sorry about that! You know how us newbies are.

As if it was yesterday   ........

Thank you   !   Well done   !