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Firefox Uses Incorrect Paper Size When Printing

When printing, Mozilla Firefox uses a paper size that is different to the size specified in the printer driver, eg. it attempts to print at “Letter” size when the printer is configured to “A4”.

This occurs because Firefox stores the printer setting in its configuration file, and subsequently ignores any settings in the printer.

The incorrect size may be stored if you install the US version of Firefox (which uses Imperial sizes) instead of the UK version of Firefox (which uses metric) — or vice-versa.

It may also happen if you print a webpage from Firefox before the printer driver has been configured with the correct paper sizes.

Firefox does not provide a simple GUI function to alter the paper size used by each printer. There are a variety of methods to rectify.

  1. Open Firefox and enter about:config in the address bar. This takes you to the full listing of settings within Firefox. Alter those starting with user_pref("print. as appropriate.

  2. Manually remove the printer settings from prefs.js. Open the file with Notepad from %APPDATA%\Mozilla\Firefox\Profiles\<Profile> (eg. C:\Users\Arthur\AppData\Roaming\Mozilla\Firefox\Profiles\<Profile>) and remove all the lines beginning with user_pref("print. Then save the file. This will preserve all your settings except the printer information.

  3. Delete prefs.js completely. This will reset Firefox to the default settings.

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