Netscape 6 will ignore both Internet Explorer and Netscape Navigator 4 proprietary HTML tags -- as well as tags from older authoring tools. Thus a page may not display in Netscape 6 as it does in Internet Explorer 4 or Netscape Navigator 4. Use of the document.layers method, which only Navigator 4 ever supported, is probably one of the most commonly encountered problems.

For more information, see Updating DHTML Web Pages for Next Generation Browsers, which tells you how to update your pages for Netscape Gecko as well as how to respect the standards for IE browsers.

An HTML page can be quickly checked for the use of proprietary HTML markup by submitting the page to the W3C's HTML Validator using the HTML 4.01 DOCTYPE. We will have more to say about DOCTYPEs later below, but essentially the DOCTYPE is supposed to indicate to a browser what version of HTML is used in the page. The HTML Element Cross Reference provides a list of all HTML Elements supported in Netscape 4, Netscape 6, Internet Explorer 4 and up and can be used to determine which HTML Elements are supported by all browsers.

Often, the process of detecting a browser causes problems. If the browser's user-agent string is simply detected as "Netscape", users of Netscape 6.x may get served content specifically designed for Netscape Communicator 4.x. Please see how to detect Netscape 6.x browsers and Browser Detection for a better approach to detecting browsers.

Pages not loading may also be symptomatic of a server issue.

If browser sniffing is set up properly yet the content is still not working in Netscape 6, this could point to a DOCTYPE issue. Netscape 6, Internet Explorer for the Macintosh and Internet Explorer 6 all use a technique called DOCTYPE sniffing to determine if a page is to be laid out in a fashion compatible with the older browsers or if it is to be laid out in a fashion compatible with the W3C standards.

While DOCTYPE sniffing is a useful means of continuing to support the older browsers, it can be a problem for newer browsers such as Netscape 6 if an inappropriate Layout mode is specified. Read more about DOCTYPEs and Layout modes for Netscape 6 compatiblity.

Authors have developed many techniques which take advantage of idiosyncracies in particular browsers to achieve the desired effect, and may be relying on coding standards of older, obsolete tools which use proprietary code. This can cause problems in Netscape 6 since it implements the standards strictly. Some common practices which result in problems with Netscape 6 include the following:

• Bad layout: Dynamic scripts generated by Macromedia Dreamweaver versions 2 and 3 are outdated and do not utilize W3C standards.
• API problems: Older versions of "cross-browser" APIs in common use around the web such as DynAPI are obsolete. Only the latest versions of these APIs can have any hope of being compatible with the latest browsers
• Layout/style problems: Incorrectly nesting FORM elements inside tables cause problems both when parsing the page and when applying the CSS styles.
• Backwards compatibility: Incorrect use of XML Empty Tag notation can hinder backwards compatibility of code.
• Broken stylesheets: CSS Class ID values treated as case-insensitive are properly case sensitive and must be treated as such.
• Broken links: Relative URLs coded for older browsers that supported the INVALID use of http://path/ for URLs relative to a web server's root directory must be of the form /path/file.html for Netscape 6.
• Broken "back to top" links: Missing <a name="top"> tags, which previously were "forgiven," now need to be included for "Back to Top" links to work.
• Broken image maps: Image maps with spaces in the names like "office locations" must instead be one word like "officelocations."

(read more about problems and solutions)

Netscape is working to ensure the following popular plug-ins are compatibile with Netscape/Gecko. The code for these plugins is the same as for Netscape 4.x other than where exceptions are noted:

• Macromedia Flash (not currently scriptable; Macromedia is working on fixing this)
• Macromedia Shockwave
• RealNetworks RealPlayer
• Although RealPlayer is one of the few embedded media players that exposes itself to scriptability (e.g. using DHTML and JS to "talk" to the plugin), on Mac OS this feature isn't optimal for RealPlayer 8 in Netscape 6.0 and up.
• Due to a RealPlayer problem, with rtsp:// protocols on Netscape 6.1 and later, the RealPlayer is invoked outside of the context of an embedded player (despite the use of the 'embed' tag).
• Apple Quicktime
• Quicktime 5.x is not "scriptable" -- e.g. the plugin doesn't expose JavaScript methods for DHTML authors to manipulate the plugin.
• Adobe Acrobat
• EA Games
• iPix
• Microsoft Windows Media Player
• Windows Media Player can be made to work in Netscape 6.x as both a plugin (embedded inside the browser via the HTML 'embed' tag) and a helper application (outside the context of the browser), with a few important caveats. The WMP is not scriptable in Netscape 6.x. Netscape recommends the Microsoft Windows Media Player 7.1 installer, which recognizes Netscape 6.x as well as the other browsers on a user's system. (read more)

Blank pages: This may occur due to the use of TLS/SSL 3.0 Intolerant Servers. A number of Netscape 6 and Mozilla users have reported that some secure sites -- typically sites featuring online transactions or online banking over the https protocol -- do not display any content at all. The connection seems terminated and a blank page is displayed. This is the main symptom of the problem when Mozilla based browsers encounter TLS/SSL 3.0 intolerant servers.

Other common problems:

• Downloads malfunctioning due to incorrectly specified MIME types
• Faulty implementations of HTTP
• Faulty implementations of SSL