Another vote for "excellent" Rated 5 out of 5 stars
Easy Add-On. Good recommendation for your first Add-On. Once you start adding-on, you'll never stop.
After the add-on is installed, you'll notice that no buttons have been added to your toolbar. That's because there's One More Step...
Right Click on an empty spot on the toolbar to open the "Customize Toolbar" window. Scroll down to the bottom of the window to find the new "Zoom Toolbar" buttons. Drag the Zoom Toolbar buttons to a happy place on your toolbar, where you'd like the Zoom Toolbar buttons to live. The Zoom Toolbar buttons will now be gone from the Customize Toolbar window, and will appear instead on the toolbar.
Close the Customize Toolbar window, and you're in business.
(By the way, while the Customize Toolbar window is open, you can drag All of the elements in the toolbar to different locations [on the toolbar] of your choosing. THAT will keep you busy for a few evenings.)
Any other Firefox windows that were already opened before adjusting the toolbar layout will not immediately be affected by changing the toolbar on that first window. But any succeeding window that you open will include your new Zoom Toolbar buttons, and any other adjustments you made to the layout of your toolbar.
There are three Zoom Toolbar buttons -- Zoom In, Zoom Out, and Reset. At first, I was disappointed that there was not also a button for Zoom Text Only (an option on the menu), but I soon realized that I don't toggle that state very often, and I don't need it to be on the toolbar. (I could even do without the Reset button.) So I'm happy with the three buttons.
Depending on your position as you're curled up with your notebook, sometimes it's easiest to change the text size by clicking on a Zoom Toolbar button a few times; sometimes it's easiest to hold the Ctrl button with one hand and spin the mouse wheel with the other hand; sometimes it's easiest to hold the Ctrl button and click the + or - with the other hand; and it's never easiest to adjust the text size using the Firefox menu. Certainly, every webpage needs to have its text size adjusted for maximum comfort, and when I'm on the notebook, the Zoom Toolbar buttons are the way I usually use to adjust the text size.
If you adjust the text size on one window, any other window you switch to afterward will get the same adjustment, regardless of whether it needed its text size to be adjusted or not. That is the way Firefox 3.6.9 behaves -- it is not caused by Zoom Toolbar. Of course, any undesired text-size adjustments on subsequent windows can be easily un-adjusted with the Zoom Toolbar buttons. It's not a big deal, but allowing each window to have its own zoom-level will take an update from Firefox -- it's not something that Zoom Toolbar can fix, methinks.