16.04 with Firefox issue

Hi,
I have an issue regarding Firefox on Ubuntu 16.04. Awkward to explain but I'll do my best.....

I have the Firefox icon locked to my Launcher. Clicking this correctly opens FF. I then open the bookmarks (Bookmarks menu / show all bookmarks) from within FF and can open any number of pages in tabs.

Past behaviour used to be that if I then clicked the FF icon in launcher FF opened a number of small windows on the desktop, each corresponding to an opened tab including the bookmarks page and I could select (click) the tabbed page I wished to bring to the front. Bookmarks opened in a separate window on screen when clicking the FF icon. This made reaccessing the bookmarks easy.

Since upgrading to 16.04, I can now only get back to the bookmarks (now called library) by right-clicking the FF icon in launcher and selecting "Library" from the drop-down list. (Or re-opening them from the top menu) This is inconvenient and for me slows down my working. It used to be that bookmarks opened in a separate window on screen when clicking the FF icon.

Can anyone help with any aspect of this behaviour? Is it a "new feature" of 16.04 or FF 45.0.2., or is it something I have done to cause said behaviour? More importantly, can anyone help me correct it...?

Many thanks.

Pat.