You cannot organize bookmarks directly on Firefox for Android. However, if you use Firefox Sync to sync with Firefox for the desktop, you can organize the bookmarks on the Desktop. The desktop organization is pretty good.

To set up Firefox Sync, see here: https://support.mozilla.org/en-US/kb/how-do-i-set-up-firefox-sync

To organize your bookmarks on the Firefox desktop client, see here: https://support.mozilla.org/en-US/kb/bookmark-folders-organize-your-bookmarks

That's a stupid answer to there question, how is it going to organize his phone's bookmarks if you sync it to your desktop. This is the biggest problem with Firefox's app on the Android is you can not organized anything with your bookmarks. I wish you can actually create folders and be able to add bookmarks to your folders. I think this is one of the biggest things that I can't stand about the Firefox browser. you can't organize your bookmarks especially when you have quite a few of them.