IEInternals

A look at Internet Explorer from the inside out. @EricLaw left Microsoft in 2012, but was named an IE MVP in '13 & an IE userAgent (http://useragents.ie) in '14

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  • Blog Post: Networking Improvements in IE10 and Windows 8

    Internet Explorer 10’s networking code builds upon the performance improvements in IE9 ( caching , overall networking ) to help ensure that IE10 loads pages as quickly as possible. In IE10, we identified a few key areas for improvement based on customer feedback, code inspection, and telemetry...
  • Blog Post: Use IMG tags only for Images

    First, a bit of background. When web developers are optimizing the performance of their sites, often they try to use their homepage to pre-cache resources that will be used on later pages. They might do so by kicking off "pre-fetch" resource downloads after the content required by the homepage itself...
  • Blog Post: Understanding Enhanced Protected Mode

    Last week, Andy Zeigler announced the introduction of Enhanced Protected Mode (EPM) over on the IEBlog. In today’s post, I’d like to provide further technical details about EPM to help security researchers, IT professionals, enthusiasts, and developers better understand how this feature works...
  • Blog Post: The Hazards of Browser Quirks, continued

    My First Law of Browser Quirks was introduced a while ago : If there’s a way for a site to take dependency on a browser quirk, and break if that quirk is removed, it will happen . The Second Law of Browser Quirks is: If there’s a way for a site to combine a set of browser quirks to yield...
  • Blog Post: Understanding Once-Per-Session Cache Validation

    Last year, I wrote about the IE9 improvements in heuristic expiration , which apply when a server fails to specify how long a cached resource should be treated as fresh. Heuristic Expiration works by calculating an implicit freshness lifetime from the Last-Modified timestamp on the cached resource and...
  • Blog Post: Avoid “Do not save encrypted pages to disk”

    Internet Explorer has an Advanced option named Do not save encrypted pages to disk . By default, this option is unchecked (except for Windows Server systems) and I recommend you leave it that way. In IE9, this option does exactly what it says it does—resources received from HTTPS URLs...
  • Blog Post: A Primer on Temporary Internet Files

    On Windows Vista and above, Internet Explorer’s Temporary Internet Files are maintained in two isolated WinINET cache containers. One cache is used for sites loaded in Protected Mode (Internet Zone and Restricted Zone) and the other cache is used for sites loaded outside of Protected Mode (Trusted...
  • Blog Post: What is msimgsiz.dat?

    Inside your Temporary Internet Files folder you likely have a file named msimgsiz.dat . If you open this file, you’ll find that it contains nothing but binary goo: Over the years, many people have asked or speculated about what this file is used for, and the answer is actually quite simple...
  • Blog Post: The Hazards of Relying upon Browser Quirks

    While many web developers find subtle browser behaviors baffling, often browser developers are bewildered by web content. Yesterday, we ran into an interesting site compatibility problem that occurs in the latest internal version of IE9. The site in question is a popular site which uses a Flash applet...
  • Blog Post: The Performance Impact of META REFRESH

    Some sites will utilize the META REFRESH directive to perform a client-side redirection. In general, this should be avoided in favor of other redirection types, for instance, a server-side redirection (HTTP/3xx) or by using JavaScript. Using META REFRESH creates a potential performance problem in IE...
  • Blog Post: HTTPS Caching and Internet Explorer

    From time-to-time, I get questions about Internet Explorer’s behavior when it comes to caching of HTTPS-delivered content. It comes as a surprise to many that by-default, all versions of Internet Explorer will cache HTTPS content so long as the caching headers allow it . If a resource is sent...
  • Blog Post: Use Sensible Long-Lived Cache headers

    As some of you might expect, I watch all of my network traffic when I browse the web—you never know when you’ll see something interesting. This afternoon, for example, my curiosity was piqued when I noted that as I browsed around the Zune website, my browser issued conditional HTTP requests...
  • Blog Post: Internet Explorer Cannot Download https://something

    Earlier today, I was asked to troubleshoot a secure site where file downloads were always failing . Having seen this problem many times often over the years, I immediately suspected that the web developer wasn’t aware that if a user tries to download * a file over a HTTPS connection, any...
  • Blog Post: IE8's Native XMLHttpRequest Object Restrictions, Bugs, and Notes

    Protocol Restriction Internet Explorer's native XMLHTTPRequest object permits requests to HTTP and HTTPS only; requests to FILE, FTP, or other URI schemes are blocked. Update : IE10 XHR supports CORS . Method Restriction The object permits only the following HTTP methods: "GET", "POST", "HEAD", "PUT...
  • Blog Post: Internet Explorer's Cache-Control Extensions

    Some time ago, I wrote a summary of how Internet Explorer’s cache works . At the time, I left out mention of the two cache-control directives introduced by IE5: pre-check and post-check . These directives enable a “background update” mechanism where a cached resource is reused while...
  • Blog Post: Vary with Care

    About the Vary Response Header As described in the HTTP/1.1 specification ( RFC2616 ), the Vary response header allows a cache to determine if a cached (still fresh) response may be returned for a subsequent request, based on whether or not the new request's headers match those that were sent when...
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