Print Preview Bug in Mozilla



Before a user prints a page from the Internet in the Mozilla browser, s/he can have the program display a 'print preview', a feature that shows how that Internet page will print. Mozilla does not correctly display the page in Print Preview, however, in that the page appears entirely different from how the printer actually prints it. FireBird displays the text in an almost unreadable format, with characters overlapping other characters. This can be misleading to users, as they could think that either the page will not print correctly or that their program has been corrupted.

Application Description

Mozilla Internet Suite is a free web suite designed by Included in the suite are an Internet browser, an address book, a mail and newsgroup reader, and a program debugger.

Test Design

This example demonstrates the use of Function testing. In Function testing, we evaluate the application by locating and isolating functions, then interacting with the functions and observing how well each can perform its task.

In this presentation, we are looking at the Print Preview function, which displays the printable version of an Internet page. We want to verify that this function works correctly, is easy to use, and has an intuitive interface (meaning that it operates how users would it expect it to and that it can anticipate what users would like to accomplish).

Function testing is a powerful testing technique in that we can see exactly what one function outputs from a specific input. In this presentation, we are giving an input of an Internet page, and we are expecting the function to display how a printer would print that page. We can directly observe if the function does this correctly.

Performing the Test

  1. Open the Mozilla browser and maximize the program window:

  2. In the address bar, type
  3. In the Yahoo! search box, enter a search field, such as "bugs in mozilla" and press enter to search:

  4. When the search results display, click on File->Print Preview.


As we can see, it is difficult to determine how this page would print out. We know how the original page looked, and so we therefore know that the way that page was displayed in the print preview is different. The text is almost unreadable because the formatting of the page caused words to overlap. Printing the page allows us to see that the page will still print out correctly, and assures us that the error is fortunately only with the Print Preview function. This was a confusing bug, though, as without printing, users may think that the page is unprintable or that something is very wrong with their Internet browser.

This bug is important because most users will use the Print Preview function before printing a page to make sure that what they want is being printed correctly.

This bug is not critical and does not affect the program in any serious way, but it is misleading and can cause many users frustration.

Function testing allowed us to quickly and easily find this bug because we simply targeted one function with as few other variables as possible. By working with this one function and all other options as default, we could see exactly how this function performed with the text that we had.

Similar Tests/Additional Notes

You might also be interested to download the new Mozilla browser, FireFox, and perform the same test. Since FireFox is built off of the same code as the Mozilla browser this bug is still an issue, but there are some distinct differences between this bug and the one in FireFox.

Similarly, this test was performed using Yahoo!'s website. Try it with other sites to ensure that the bug is not just with the Internet pages' coding.

Configuration Notes

Testing Mozilla's Internet Suite v1.4.1 on:

Created 31 May 2004 for the CSTER

All images and written material ©Copyright Sam Oswald 2004

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