You have to add at least one tag to a bookmark in the Bookmarks Manager (Library) to make the Tags field appear.

• https://support.mozilla.org/en-US/kb/categorizing-bookmarks-make-them-easy-to-find

Wow! Thank you so very, very much cor-el - I wish I had asked this two weeks ago. I've tried everything I could think of.... Googling, Firefox settings etc. After reading your post, it took less than 1 minute to finally see the "tag" option! I really thank you for your time and kindness. So appreciated!

You're very welcome.

I'm shocked by the what the solution to this is. The tag field should be visible by default, and arguable it shouldn't be hideable.

If someone thought it provided a good user experience to enable tagging in the UI by opening a more obscure hard to reach library menu and manually adding your first tag, they are dead wrong.

I have been mystified by the "absence" of such a useful feature, and it's there, hidden in the UI by default.

Epic design fail.