If your Internet Explorer browser just slowed down (I mean, slowed down to something slower than the usual snail’s pace, there is a known reason for it. Last week, Microsoft released two security patches in their regular updates that you have probably installed, either knowingly or automatically. Microsoft already reports that, “web applications that implement consecutive modal dialog boxes may cause Internet Explorer to become slow and unresponsive over time.”
Microsoft issued the hotfix for Internet Explorer versions 7 through 11—basically every major version.
Fortunately, Microsoft was quick to issue a fix to their fix. But you will have to download it manually from Microsoft’s support page.
Once you run the update, you will be asked to reboot. Once you do, the update will be applied and your browser should return to it’s “normal” slow performance rather than the “unusually” slow performance you’ve experienced since the updates.