Hi all. Problem solved by TABMIXPLUS addon. As you can see on the picture, the check box sais Prevent double click on tab-bar from changing window size It works like a charm...

Strictly speaking, your approach is not fully suitable for my question, because I wanted to do without any additional add-ons. That especially regards to TM+ , which can be rather heavy and buggy and can drop into conflicts with other extensions.

p.s. I've founded another temporal solution, which implies creating another bar on the top, putting all wanted items on it and hiding both Menu Bar and Navigator Toolbar (so consequently remain only Bookmark toolbar and the new created one).

You can move the tab bar out of the title bar.

You can set the pref browser.tabs.drawInTitlebar to false on the about:config page to prevent that from happening too easily.