Component properties are not rendered in IE8

In IE8, the component properties are not rendered. The javascript console logs an error.

Steps to reproduce:
1. use IE8
2. login to the CMS
3. navigate to the English website in the channel manager
4. click 'Edit Channel'
5. click on any component

Expected: the component properties for the selected component are shown and can be edited
Actual: the component properties window is shown, but the properties are not. The script console shows the following javascript error:

Object doesn't support this property or method (_cmsinternal, line 40790433, character 13)

The exact line on which the error happens cannot be traced.