Hi, open the 3-bar menu > Customize, and if you can see the zoom button, simply drag it to a toolbar and the location of your choice, then Exit Customize to save. If the button isn't there, click on Restore Defaults.

More here - Customize Firefox controls, buttons and toolbars

There is also an Add-on that you might like - Page Zoom Button. With this you can zoom by pointing to the button and turning the mouse wheel.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you.

nick890 said

Hi, I used to have a plus '+' and a minus '--' sign up top left of browser just right of the back space arrow level with address bar. I've lost it some how but don't know how to get it back . As I have poor eyesight I really miss it. Any help please. Running win 7 ultimate 64 bit Mozilla foundation my default browser. I do use Ctrl + but I also like those symbales back if I can. Thank you. Nick

Thank you that worked. Funny, as when I rebooted the + 100% - showed up again at the top of my 3 bar menu so I was able to just drag it from there. I tried the other single button but you really need a 3 button mouse.