HTML popup page and file upload issue

Hello,

I'm new to the Web UI testing and Telerik software.

I've a few questions regarding the FileUpload and HTML pop-up window.

Here is how I've been recording with Firefox.
1) I've navgiate to a page with 'https://testingthis.com
2) this page has the an attached-file button, which open the pop-up window with https://testingthis.com/upload/fileupload/12345
**this 12345 may change each time doing the test because my colleagues may be attaching files anytime" -> may be 2 min later, it could change to 12347... etc

My issues are
a) When the attached file is clicked and the popup window comes up, the recording does not work on any elements on the pop up page.
b) because the last part of pop-up URL changes, I cannot hard-code it by navigating to that page. I have done that by manually navigating the pop-up URL and tested with the file upload Dialogue and found it working INSTANTLY. since no one has used up my allocation, I find it working.

Anyway to solve this issue?

Thanks in advance for your help.