Firefox Freezes, If Warning Dialog Pops Up While Dragging and Dropping

 

Summary

In this example we are going to test the drag and drop functionality of Mozilla Firefox v1.0PR by interfering with it. This web browser allows the user to drag and drop HTML links or other objects on the page. If a dialog box pops up while the user is dragging an object, the application freezes. (Source: bugzilla.mozilla.org)

Application Description

Mozilla Firefox is a web browser developed by mozilla.org. It can be used to read HTML documents online or on the local machine, check email, download files, and others. It has built in Tab browsing, pop-up blocking, image blocking and so on (Source: www.mozilla.org).

It also allows the user to drag and drop HTML links in text boxes. The result is that the address of the link is the entered into the text box.

The application usually informs the user about problems using this type of dialog boxes:

Test Design

This example demonstrates the use of Interference Testing. We will start a process and then interrupt it while it is in progress.

A typical drag and drop process starts when the user presses a mouse button on an object and while holding it, starts moving the mouse. The process ends when the user releases the mouse button. A question that we might want to ask is: what happens if there is another process that executes while the user is dragging the object? Examples of processes that could interfere with the dragging process are: closing the current window, switching to another application, displaying a modal dialog box (a box that stays on the screen and claims all the user-input), and so on.

Let's focus on the example with the modal dialog box. One way to cause this box to appear is to enter 127.0.0.1 in the address bar (the connection will be refused, unless there is an http server running), or we can disable the internet connection and enter any address. We will start dragging an object so that when the dialog box shows up, we will be in the middle of the process.

We would expect that when the box is displayed, the dragging process is canceled. After dismissing the dialog box, the application should be in its original state.

Performing the Test

Note: steps 1 and 2 have to be performed without any delay in between.

  1. Start Firefox. Type '127.0.0.1' in the address bar. Before the dialog box has shown up (2-3 seconds) move to step 2.

  2. Click on one of the links in the page and start dragging it.

Results/Relevance

The "Alert" dialog box shows up as expected, but there are two unexpected side effects.

First, the box is missing the exclamation mark picture on the left.

Second, it is impossible to click on the "OK" button or the "x" in the upper left corner of the dialog box. The main application doesn't accept mouse input either.

 

At this point many users will assume that the browser has crashed and will use "End Task" to close it, possibly losing the data that is currently displayed.

The probability of a message appearing while the user is dragging an object is not very high; therefore, it is unlikely that a tester will find this bug unless he or she is applying a testing technique that is targeting this type of errors (such as Interference Testing).

Even though, the problem by itself is not very likely to occur (and there is a workaround), it could reveal a larger underlying problem to the developers.

Additional Notes

As a workaround, the user can press 'Enter' or 'Escape', which will dismiss the "Alert" dialog box, and the browser will be able to accept input again.

Configuration

Testing mozilla.org's Firefox 1.0PR on:

Created 12 October 2004 for the CSTER

All images and written material ©Copyright Georgi Nikolov 2004

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