Pressing Ctrl+K doesn't focus the appeared dialogue

When any user or admin is composing a msg, and presses Control+k to insert a hyperlink on my website, the user has to click in the field where he is supposed to type the hyperlink.

But when in the same (FF/Chrome latest version) browser, we go to and do the same/press the same shortcut, we can straigthaway type the hyperlink, which is hugely convenient and fast. While on my website, if we start typing the link, it’d be typed somewhere in the background compose window or lost.

What can go wrong here?