Microsoft Internet Explorer (MSIE) is very much the incumbent in the web browser arena. Before the arrival of Firefox, MSIE had estimates of >97% of market share. Firefox has cut into MSIE's marketshare, dipping MSIE usage below 90% in the US, and down to the 60% range in markets such as Germany.

Advantages Integration with other Microsoft products Microsoft often offers its customers good integration among its products, and MSIE is no exception. One can drag an Excel bar graph from an MSIE webpage onto an existing Excel document, or view a Microsoft PowerPoint presentation from within MSIE. Within a Microsoft-only corporate intranet, this integration is very helpful. However, for a business interacting with the outside world, the argument weakens since the foundation of the Internet is to share among different platforms. Outside users expect documents to be in platform-agnostic formats such as HTML or Acrobat PDF files.

MSIE also offers strong integration with its Microsoft operating system, though is a double-edged sword, since it contributes to its security woes.

ActiveX and VBScript support ActiveX refers to small Windows executable programs that can be run from MSIE, and VBScript is a client-side script for Windows code.

Some business have heavily invested in either developing or purchasing custom ActiveX software (and/or VBScript), for applications ranging from web-based accounting to e-learning simulators.

The Firefox team made a conscious decision to support neither ActiveX nor VBScript, since they are not accepted web standards and are often the source of the security vulnerabilities within MSIE.

Since Firefox will not likely ever support ActiveX and VBScript, businesses whose products revolve around these technologies would be better served with MSIE than with Firefox.

Still some MSIE-only webpages Since MSIE formerly had such a large marketshare, some businesses' webpages still only display correctly in MSIE.

However, Firefox's increasing marketshare has caused many companies to revamp their pages to work correctly in Firefox also.

There are several reasons. Businesses want to ensure that they can sell to the Firefox customers. Moreover, many of the users who purchase with credit cards have moved to Firefox because of the extra security for that sensitive transaction. Finally, many businesses see that it costs less to fix the pages, than to cover the "Why doesn't work in Firefox?" technical support calls support calls.

Arrives with a new Windows computer MSIE arrives installed new Windows and Mac computers; Firebird does not.

However, the initial MSIE is unpatched and thus riddled with security holes. Thus, novice Windows users are often disappointed as their computers become increasingly unresponsive with viruses and spyware.

Thus, the convenience of having MSIE preinstalled on Windows is minimal, since Firebird can be downloaded and installed about as easily as patching the initial insecure MSIE.

Microsoft has ceased new development of MSIE for the Mac, so it has decreasing usefulness on the Mac as an out-of-box browser. Disadvantages Closed source and tied to a U.S. company Closed source prevents users from reviewing the code to ensure that there are no security backdoors included in the software.

This is particularly important for Internet communication software, as the U.S. government may approach Microsoft to either divulge or include security backdoors that can be used for information surveillance, especially on foreign governments or high-risk suspects. Some governments don't want to have a foreign country's closed source software at the heart of their information network. This may partially account for the higher adoption rate of open-sourced Firefox in countries outside the U.S.

Selling of other Microsoft items and forced end-of-life Part of any corporation's mission is to maximize profits. For Microsoft, this includes selling the maximum number of its own products and services.

So to use the newest MSIE, one has to purchase a license of their newest OS. MSIE's built-in search only works with Microsoft's MSN search, versus Firefox's built-in search toolbar that uses technically superior Google as the default and is user-selectable.

Moreover, since MSIE is closed-source software, users always face the possibility of forced end-of-life of the MSIE software and anything the user has built around it.

Total cost of ownership Both browsers can be downloaded and used free of charge, so their initial cost is equal.

For technical support questions, both are widely enough used that many solutions to common problems can be found in free online public forums. Telephone support for Firefox costs $39.95 per incident, and Microsoft costs between $35.00 per incident and can cost over $200.00 for advanced issues.

However, MSIE has heavier ongoing support costs due to the nearly monthly security patches that are required. Also, there are ongoing costs from lost work time due to the poor stability and viruses when using MSIE. Finally, with MSIE requiring the newest version of their operating system, it forces the total cost of ownership to include the cost of updating all licenses to Windows XP SP2.