This bug only affects Windows users.
When an inline style is applied to the pre tag, firefox fails to print the text enclosed in the pre tag correctly. Below is an example page.
If you are running Firefox under windows, try printing the linked page. It will not print correctly.
This can happen on Windows only. All other OS are okay. Head on over to the bug if you wish to track it.
The workaround is to not use inline styles in the pre tag. Though, why would you use them in the first place?