I spent a long time trying to attach a bas module to a post in the CodeBank, but it never worked. I was using Firefox, and even after disabling all add-ons it still never worked.

Finally in desperation I tried Edge. At first it failed, but on the second try it finally worked.

Apparently the new download manager brings up a popup window? That's an issue for Firefox, which doesn't like popups in general. (I haven't seen any popup from any site in years.) It replaces the current window (with the post you're writing or editing) with the contents of the popup, displayed as a regular page in the browser tab. Further, for this full browser non-popup version of that popup, the "Select Inline" and "Done" buttons don't do anything.

Meaning when I try to attach a file using Firefox, I am physically unable to do so AND it throws away whatever post I've been writing that I wanted to attach something to.