Microsoft Silverlight

Silverlight was a browser extension that was backed by Microsoft’s .NET product on many platforms, it provided media capabilities similar to Macromedia/Adobe Flash.  Similar to Flash, it has had it’s own share of security problems over the years.

Introduced in 2007 and currently in a deprecated state. Once supported on Windows XP (IE6) to Windows 10 (IE11), MacOS and Ubuntu. Now only supported in MSIE. Edge never provided support. Modern versions of Chrome, Firefox, Safari, and Opera no longer support.

HTML Markup example:

<object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%">
<param name="source" value="MySilverLightControl.xap"/>


Using comments to ‘hide’ SCRIPT tag content – please stop this obsolete practice

Many years ago, when HTML3 and 4 were still widely used in the mid to late 1990s, it was a common practice to place HTML style comments, or in some cases CDATA comments inside the SCRIPT tag in an attempt to hide that content from browsers that could not process it. In those browsers the content (javascript source code) would sometimes be displayed on the page, making it quite a mess.

This practice is now obsolete, and often problematic as there are very few of those browsers in use today – primarily only for testing of legacy functionality.

Example of old approach

<script type="text/javascript">
// some script

NOTE: for XHTML or XML documents, the use of a CDATA style comment is still required.
<script type=”text/javascript”>


document.write() Intervention!

The use of document.write() has always been a bad “code smell” in JavaScript. Most web performance guides such as WebPageTest and Yahoo Exception Performance have warned against this practice.

In most cases, document.write() can be replaced by inserting innerHTML into an empty element after the rest of the page loads. This approach also allows the developer to “think” about how the page might react in cases where JavaScript is disabled or not available on the client.

Google has recently changed the default behavior, such that when on a slow (currently 2G) connection, but discussions have also leaned toward including any slow connection.
As such, right now, the following will occur on slow (2G) connections:

  • Chrome 53+ (warning displayed in debugger console)
  • Chrome 55+ (blocked – code will not execute, warning message will appear in debugger console)

For users on slow connections, such as 2G, external scripts dynamically injected via document.write() can delay the display of main page content for tens of seconds, or cause pages to either fail to load or take so long that the user just gives up. Based on instrumentation in Chrome, we’ve learned that pages featuring third-party scripts inserted via document.write() are typically twice as slow to load than other pages on 2G.

My advice – remove all use of document.write() for required content in your code now, as your users MAY NOT see that content if you do not.


CSS font-smoothing

You might be tempted to use the full capabilities of your browser to do things such as font-smoothing, but it’s not a good idea as it is often overused and the Browser/OS will generally do it’s best.

Both Firefox and Safari have support of this CSS attribute as follows:

font-smoothing: antialiased;
-webkit-font-smoothing: antialiased;

NOTE: If you’re using something like Glyphicons (included with Bootstrap) you might have some use for this because of the way that fonts are used for icons.


HTML5 autofill using autocomplete

Once in a while, the web development community reintroduces old ideas in a new way. Years ago, there was a concept called ECML (E-Commerce Markup Language) that added an HTML attribute to identify values in a FORM that could be auto-filled from a users “virtual wallet”. Sadly, while it was implemented on a variety of websites (mine included), it was not widely supported and disappeared.

The concept has been reintroduced as values in the ‘autocomplete’ attribute in HTML5. Traditionally this attribute was only used to prevent auto-filling of values, now it can identify which values it is related to for pre-fill.

The usual payment, address and demographic fields (and variations of each) are supported.


^<input type="text" name="ccnum" autocomplete="cc-number" value="" />


HTML5 Link Prefetching

Link prefetching is used to identify a resource that might be required by the next navigation, and that the user agent SHOULD fetch, such that the user agent can deliver a faster response once the resource is requested in the future.

<link rel="prefetch" href="" />

<link rel="prefetch" href="/images/sprite.png" />

Supported in:

  • MSIE 11+/Edge
  • Firefox 3.5+ (for HTTPS)
  • Chrome
  • Opera


HTML5 preconnect

In addition to dns-prefetch, you can take browser performance one step further by actually creating a new connection to a resource.

By initiating an early connection, which includes the DNS lookup, TCP handshake, and optional TLS negotiation, you allow the user agent to mask the high latency costs of establishing a connection.

Supported in:

  • Firefox 39+ (Firefox 41 for crossorigin)
  • Chrome 46+
  • Opera

<link rel="preconnect" href="//" />
<link rel="preconnect" href="//" crossorigin />


HTML5 DNS prefetch

I often get into some fringe areas of micro-optimizations of website performance, DNS prefetching is another one of those topics.

To understand how this can help, you must first understand the underlying concepts that are used within the communications used to build your web page.

The first of these is a “DNS Lookup”, where the domain name ( is converted into a numerical address, the IP address of the server that contains the file(s).

In many websites, content is included from other domains for performance or security purposes.

When the domain names are known in advance, this approach can save time on the connection as the lookup can fetched in advance, before it is required on the page to retrieve assets.

This can be particularly useful for users with slow connections, such as those on mobile browsers.

<link rel="dns-prefetch" href="//" />

Supported in:

  • MSIE9+ (MSIE10+ as dns-prefetch)/Edge
  • Firefox
  • Chrome
  • Safari
  • Opera


Brotli Compression

If you look at HTTP Headers as often as I do, you’ve likely noticed something different in Firefox 44 and Chrome 49. In addition to the usual ‘gzip’, ‘deflate’ and ‘sdhc’ , a new value ‘br’ has started to appear for HTTPS connections.





Compared to gzip, Brotli claims to have significantly better (26% smaller) compression density woth comparable decompression speed.

The smaller compressed size allows for better space utilization and faster page loads. We hope that this format will be supported by major browsers in the near future, as the smaller compressed size would give additional benefits to mobile users, such as lower data transfer fees and reduced battery use.


  • Brotli outperforms gzip for typical web assets (e.g. css, html, js) by 17–25 %.
  • Brotli -11 density compared to gzip -9:
  • html (multi-language corpus): 25 % savings
  • js (alexa top 10k): 17 % savings
  • minified js (alexa top 10k): 17 % savings
  • css (alexa top 10k): 20 % savings

NOTE: Brotli is not currently supported Apache HTTPd server (as of 2016feb10), but will likely be added in an upcoming release.[email protected]%3E

Until there is native support, you can pre-compress files by following instructions here…


Deque FireEyes accessibility testing plugin

I’ve done a lot of accessibility testing and development work over my career. One of the many free tools that I use in that role is FireEyes. Deque also has some commercial packages for developer use.

FireEyes adds a new tab on the Firebug tab bar and adds the ability to analyze a web site for WCAG 2.0 Level A and AA and Section 508 accessibility violations. The Stand-Alone version of FireEyes is a browser plugin to the FireFox browser. It requires that the FireBug plugin already be installed


  • Firefox 31-41

    As of 2015aug21, the current version of the extension is NOT signed and will not execute on later versions. [See my later post on this topic]

  • FireBug 2.x – Do NOT install Firebug v3 alpha as the tab will not show.

NOTE: should be on Firebug tab labeled “Worldspace Fireyes”, but does not seem to be available in Firebug3.

NOTE: if you try to download in MSIE, you must rename the .zip to .xpi, and then open with Firefox.