The good news is that Firefox now supports high resolution monitors. The bad news is that this may have the effect of making websites look bigger than you're used to. We'll show you how to use the the NoSquint add-on to change Firefox's default zoom level back to the way it was.

Install NoSquint and set the global page zoom to 80%

This should restore the previous page zoom behavior.

1. Open the NoSquint page on the Add-ons website.
2. Click the green Add to Firefox button to install NoSquint.
3. When the installation is done, you will be prompted to click Restart Now to complete the process.
4. When Firefox restarts you will see a magnifying glass in the Add-ons bar at the bottom of the Firefox window. Click the magnifying glass to open the NoSquint settings.
   
5. In the NoSquit settings window, click Global Settings. This will open an additional Global Settings window.
   
6. In the Global Settings window, click on the Zooming tab and change the Default full page zoom level to 80%.
   
   Note: This is based on Windows setting the computer default to 125%. If this is not the case on your computer, you might have to experiment with something different than 80% to get the results you want.
7. Click OK to make the change and close the Global Settings window.
8. Click OK to close the NoSquint settings window. The process should now be complete.

You may notice that NoSquint adds a + and - button to your toolbar. If you want to remove them you can click Remove toolbar buttons on the NoSquint page that opened when Firefox restarted. If you don't have that page open any longer you can always remove them with these instructions.