Is ASP.NET AJAX truly cross browser?

It is extremely useful to know the answer if you are embarking on a long term project where you plan to use ASP.NET AJAX and the project SLA demands that your web application be cross browser.

As per the official documentation, ASP.NET AJAX is compatible with most modern browsers on some operating systems and this includes the following:

• Microsoft Internet Explorer 6.0 or later versions.
• Mozilla Firefox version 1.5 or later versions.
• Opera version 9.0 or later versions.
• Apple Safari version 2.0 or later versions

The supported Operating Systems are:

• Microsoft Windows XP with Service Pack 2 installed.
• Microsoft Vista.
• Apple OSX (Intel architecture only).

The documentation is slightly incorrect when it says Apple Safari version 2.0 or later versions are supported. Precisely Safari version 2.0.4 on the Mac & above are actually supported.

ASP.NET AJAX can run with the default security settings for the above browsers. If browser security and privacy settings are set too high, JavaScript may be disabled. It helps to have a plan on how to tackle users of your web application whose browsers cannot access AJAX-enabled content.

Is the AJAX Control Toolkit cross browser?
I have not seen any authoritative documentation that says controls in the community driven Toolkit work fine in the browsers & OSs listed above that support ASP.NET AJAX.

In the CodePlex Issue Tracker for AJAX Control Toolkit, if you search for "Firefox" with "Open Issues" checked you will notice issues with some controls.

Rant/Diversion - In the Issue Tracker, there is no mention of the year alongwith the dates on which posts/issues were logged.

I wish there was a browser compatibility chart in the description of each control at the ASP.NET AJAX Control Toolkit sample website like the cute one they have on the FCKeditor website.

Is it a good thing to force visitors to use the specific browsers or browser versions?
It's not a perfect world & in my opinion, it may not be feasible to please everyone considering the complexity of browsers. A browser may have multiple versions and it may run on different operating systems & there may be major compatibility issues across versions & OSs. There were serious issues between the Releases of Netscape version 4. A web page that works in IE 5 for Windows may not work the same in IE 5 for Mac.

Website visitors should be encouraged to use newer versions because they generally have enhanced performance, security & better standards compliance. At the same time the web application must also degrade gracefully to satisfy users who may not have the suggested browser.

Before taking a technological decision, it's relevance to the target audience should be taken into account.