javascript error instead of inserting image

Image isn't inserted into textarea, but javascript errors are generated.

How to reproduce:

1. Use Debian's FF (iceweasel 2.0.0.13).
2. Install image and image assist modules. Upload one image.
3. Create page, edit it.
4. Enter textarea, place cursor somewhere,
5. click image-with-plus-sign icon, new window(let's call it window-2) will appar.
6. click on image from list of images in that window-2 Page with options will appear (in window-2)
7. click "Insert"

RESULT:

In main window - no changes. In window-2 - gray blank area below "Properties: Change how the image.....". I see 2 javascript errors in javascript console:

uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLTextAreaElement.selectionStart]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: http://pagema.net/sites/all/modules/img_assist/img_assist_textarea.js :: insertToEditor :: line 90" data: no]
[Break on this error] undefined

uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLTextAreaElement.selectionStart]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: http://pagema.net/sites/all/modules/img_assist/img_assist_textarea.js :: insertToEditor :: line 90" data: no]