This is a bizarre one. I can't think of a reason why it wouldn't work only in this specific set of circumstances.

I have an autocomplete field. It's an Entity reference to User entities.

In Firefox and IE the autocomplete always works. In Chrome and Opera autocomplete does NOT work, except for admins.

I have stepped through the JavaScript with a debugger and it is correctly fetching the list of users and creating the popup and populating it, but for some reason it's being shown very far down the page (usually offscreen).

Comments

On further investigation it seems that maybe Bartik theme is somehow at fault. Autocomplete always works with the admin theme, which is why it works for admins, but in Chrome and Opera the autocomplete popup is appearing off the screen for Bartik.

Edit: it turns out the popup also appears in the wrong place in Firefox, but at least it's visible. It appears above and to the left. Something to do with Bartik is making the positioning of the autocomplete popup wrong. It is OK in IE except for the throbber can always be seen just below where it normally is.

I had the same problem. thanks you ! :)