Thanks but it does not work with Thunderbird or it my be my mouse that just scrolls the page still.
But if I hold down the CTRL key and click on the - or + I can make the font smaller or larger.
Also you can get this Extensions
Text size toolbar that I use that works great. You click one to make it bigger and the other to make it smaller with each click and then the one on the right gives you back your default.
Works on Firefox and Thunderbird and I use it a lot.