Please check this out: https://support.mozilla.org/en-US/questions/975442. It might be helpful for you.

You can also try to open a new window to see if it work better in that new window.
If it does then close the not working window and close and restart Firefox to see if you keep things working.

Thanks for the very prompt replies. I checked through the thread and tried some of the suggestions without any luck. I can open new windows but the toolbar and tab issues remain.

I notice that several people have problems displaying the bookmarks toolbar: my problem is slightly different in that I can't see any of mine!

Curiously, although I can see new tabs and some of the toolbars in safe mode, but when I disable all the add-ons and run in normal mode, the problem is still there. I'm going to try deleting the add-ons completely one by one to see if I can identify a conflict.

After my previous post, I started deleting the add-ons one by one and chose one that provides a tree-style tab as the first since it was related to the problem and bingo! - as soon as I restarted FF, the problem had gone. I re-installed the add-on and started FF again, thinking that the problem might return but it didn't.

I guess the add-on must have become corrupted in some way that conflicted with FF and prevented me from seeing the toolbars and new tabs on the display. Initially, I was inclined to reject this possibility as the problem didn't go away when I disabled the add-ons, only when I deleted it entirely.

Moral: disabling an add-on doesn't necessarily cure a problem; sometimes you need to remove it completely.

This is probably obvious to many members but I'm a software user, not an engineer :-)