I just found the solution to a problem with Opera web browser. When I added more tabs than could fit the width of my screen, the additional tabs weren't visible in the tab menu. I would prefer the width of all tabs to be adjusted so that all tabs would fit in the menu.

The solution to this problem was to right click on the tab menu, select "Customize" and "Appearance", change the "Wrapping" setting to "No Wrapping". That's it!