The problem was that
codeSpecialProject.uniqueID
returns the name tag of the control not the id tag.
IE 7 has an issue that allows document.getElementById to also identify controls by their name tag, not just their id. Due to this issue (bug) of IE 7, it worked in IE 7, but failed in all other browsers.
More details on the issue here.
Solution
The ClientInstanceName of the PropertiesTextEdit (which is a ASPxClientTextBox)
<PropertiesTextEdit Width="100%" ClientInstanceName="codeSpecialProject">
</PropertiesTextEdit>
created for use in JavaScript
codeSpecialProject
has several client methods. To change its text, one should use the following method:
codeSpecialProject.SetValue('text')
More on devexpress client methods here.