One under the other, look at the screen cap.

Sorry for the delay responding, I thought I would be notified for each answer.

Here is what the Firefox addon looks like:

https://postimg.org/image/ge0nk54ft/

Hi,

I used Opera a long time, it had all that was needed without add-on, especially the 2 pane bookmarks.

Then, Opera was destroyed, replaced with a bland and featureless version, and I switched to Firefox.

Over time, Firefox has become bloated and slow, but it does have a 2 pane bookmarks add-on, and Opera still does not, which makes it unusable when you have to deal with thousands of bookmarks in hundreds of folders.

So, after all this time, why no 2 pane bookmarks add-on for Opera? They INVENTED it, destroyed it, and never replaced it with anything remotely as useful