You can zoom the currently displayed message using the same approaches as you would in Firefox:

• Hold down Ctrl and tap + to enlarge
• Hold down Ctrl and tap - to reduce
• Hold down Ctrl and tap 0 (that's a zero) to return to the default size
• Hold down Ctrl and move the mouse wheel away from you to enlarge, and toward you to reduce

More info: https://support.mozilla.org/en-US/kb/keyboard-shortcuts#w_message-functions

I suspect there might be an add-on to do this for you automatically, but I wasn't successful in finding one.

I too, as many others, have trouble with the small font on incoming e-mail. I understand that ctrl+ will zoom in which works fine but I would like to have a zoom in and zoom out icon on the toolbar so I don't have to use the keyboard. Since they don't seem to exist is it possible to build my own?

Zoom Button for Thunderbird 'Zoom in, zoom out, and reset zoom with one toolbar button. Works in the Compose window too.

Also see Theme Font & Size Changer Theme Font & Size Changer lets you change the global font size and font family used for the user interface in Firefox. Design your browser with your favorite font. Works with Thunderbird and SeaMonkey too.

I tried that add on but it doesn't do what I want. I read e-mails in a separate window and the "Zoom Button for Thunderbird" doesn't add that button to the customize icons group for a separate read window.

I was not aware of that. I'll look into fixing it. Thanks, and sorry. :)

The latest version of Zoom Button for Thunderbird (0.0.8) addresses the issue that you noted. "doesn't add that button to the customize icons group for a separate read window''

I hope this works out for you and thanks for the heads up about the problem.

If you have other issues with that add-on, feel free to send me a private message here, or click on the Support E-mail link in the right hand column of the add-on's page.

Works great. Thanks for the quick response.