For quite a few months one of the pages in my custom project planning and tracking application would not open any pop ups in IE9 but would work fine in other browsers. The simple work around was to open that page in Chrome. Finally, when IE10 came, I decided to troubleshoot the issue.
The issue reported in the developer console was:
Ultimately, with the help of the following URL it was discovered that the issue pertains to bgiframe using a regular expression which errors out in internet explorer (because of the faulty regex for IE9+).
All that was done to resolve the issue was replace
$.browser.msie && /6.0/.test(navigator.userAgent)
$.browser.msie && /msie 6\.0/i.test(navigator.userAgent)