I'm not sure what exactly you mean by saying "I routinely try, in several browser, to find a tab among open tabs, a bookmark among open bookmarks," but if you -

I'm not sure what exactly you mean by saying "I routinely try, in several browser, to find a tab among open tabs, a bookmark among open bookmarks," but if you - like me - keep hundreds of open tabs in a couple of dozen windows and you can't find the tab you need at the moment, then you may be happy with the Firefox extension tabFx...