Suddenly all previously opened tabs disappeared and I can only open one tab at a time.

Two days ago while using Firefox my interface/window changed. Whereas before I could have many, many tabs opened across the top of my window, suddenly they are gone. I now have one place where I can put in my new search and no ability to easily access formerly opened tabs. So if I am in my gmail account I can open different tabs/searches and go back and forth between them and my gmail or between search and search. I like to keep open tabs that I want to return to easily - things I haven't completed reading, things I need to get back to to fill out something, etc. Now I can't get to them easily. I know that there is a history, but I am may be wanting to find a tab that I opened two weeks ago and don't remember the date or the name. If they were still opened in this bar across the top (and I am not referring here to bookmarks), I can find them. When I no longer want them opened I delete them. I don't know if this problem is due to the recent Firefox update or if I did something by mistake that caused this. It is making my use of Firefox as my browser very cumbersome and impractical. I also can't spend hours and hours reading through Firefox materials to see if I can find a way out of this problem. Ideally, if I could speak to an actual help desk person, that would be great. I am an 80 year old woman who would like to be able to keep up with all my interests and activities and not being able to use Firefox in the way that I have will really be an obstacle. Thank you for any help that will be offered. Louise