Unfortunately the Internet Explorer default settings are not very friendly to AJAX heavy applications.

Microsoft provides a Knowledge Base article with the exact settings for IE 7 & 8, the instructions for IE 9 are the same for 8.

http://support.microsoft.com/kb/282402

Checking FireFox looks like their default settings in version 9 are 15, so I would recommend starting with 10 or 15 but don’t go too much higher without a good reason :)

Reference:

• http://support.microsoft.com/kb/282402