As all of you Vista users surely know, IE9 is the last version of the MS supplied browser that can be installed on that OS.
It has several prerequisites, notably KB948465 (SP2 for Vista SP1), KB971512 (Windows Graphics, Imaging, and XPS Library) and KB2117917 (Platform update supplement for Windows Vista); you can read more here.  MS had continued patching security vulnerabilities in IE9 on Vista SP2 via "Cumulative Security Updates for Internet Explorer 9 on Windows Vista SP2" up until Vista's EOL on April 11th of this year (update KB4014661).  MS will continue patching IE9 on Windows Server 2008 SP2 (as, again, it's the last version installable there, too) until that product reaches its (Extended Support) EOL in 2020. If you have been following our Server 2008 Updates on Windows Vista thread, then you should have already installed follow-ups KB4018271 (May 2017), KB4021558 (June 2017) and KB4025252 (July 2017). For the rest of this post I'll assume your Vista SP2 OS (ergo IE9 copy) is fully updated even with post EOL updates intended for WS2008SP2; e.g. on my setup (Vista SP2 Home Premium 32bit), "About Internet Explorer" looks like:  For those of you out there with an intention to using IE9 as your main browser on Vista, sadly, you'd have come to the conclusion it's only half-usable currently, at best; this is a result of: 1. Most modern sites have removed support for IE9 completely, via UA string sniffing: Somes sites (like Youtube) offer a workaround, for others it may be necessary to spoof the actual UA string as one from a later OS+IE version (e.g. via the "Set UA String" IE addon). 2. Many sites have moved to recent web design, so they don't render correctly (if at all) in IE9, even in "Compatibility View" (well, actually, this is to be expected; CV means the site was optimised for IE8-); FWIW, even MS pages don't display correctly now in IE9 . 3. A third scenario I find quite irritating is that many sites fail to load at all in IE9 if they use the HTTPS protocol; with the recent move of many major sites to the more secure, encrypted, HTTPS, "allegedly" to increase user privacy and security, I found the list of "secure" sites not opening in IE9 growing at a high rate; of course there's always Firefox, but it's IE9 we're discussing here...  Upon investigation, I discovered this is due to IE9 on Vista only supporting TLS protocol v1.0; this is considered by today's standards no longer secure enough, so many sites using HTTPS have moved to the more secure versions 1.1, 1.2, even to 1.3!  Fortunately, a recent MS update (intended for the WS2008SP2 OS) can be applied on Vista SP2 that will implement TLS 1.1/1.2 support on Vista's IE9, too! ; I have spoken about this important update here. 1. Install then KB4019276 2. Reboot the Vista machine 3. After restart, launch the Registry Editor (regedit), preferably as Administrator. 4. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AdvancedOptions\CRYPTO\TLS1.1 5. Delete the "OSVersion"="3.6.1.0.0" subkey; BTW, I don't know which WinOS that string refers to (Win6.1=Win7) 6. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AdvancedOptions\CRYPTO\TLS1.2 7. Again, delete the "OSVersion"="3.6.1.0.0" subkey. Exit Registry Editor. 8. Launch IE9; Tools -> Internet Options -> Advanced tab -> Scroll all the way down to "Security": Prior to KB4019276 and registry manipulations, only "Use TLS 1.0" had been available on Vista; you should have already unchecked the older "Use SSL 2.0/3.0" options, to avoid being targeted by "POODLE" attacks; uncheck "Use TLS 1.0" (optionally also "Use TLS 1.1") and check "Use TLS 1.2". 9. Click Apply, OK, then exit IE9. 10. Upon restarting IE9, you'll find you can now visit all those sites that previously would not load due to unsupported TLS protocols: 10. You can verify further that indeed 1.2 is being used during server-client negotiations via specialised sites or via IE9's native GUI: I honestly hope you'll find my post to be of value; enjoy your more secure (than ever before?) Vista OS!