IE8 addon, coded in javascript

Question

I've made a small IE8 add-on, the button in the tools bar appears as it should be, but once it is clicked, gives error:

Script: secret
Line: 1
Char 8
Error: Expected ';'
Code: 800A03EC
Source: Microsoft JScript compilation error.

The .js was saved under utf-8, checked with three complicators, there are no syntax errors or ';' missing in there. The script is of 20 lines, and pretty much all of them are getElementById() functions. The first line is a mirror to: var secretVar = document.getElementById('secretId').value;

Yes, I tried content.document.getElementById('secretId').value;

but the same error appears.

Is there something specific that I am missing in the script? Should there be an additional line to target exactly the page on my IE?