Steps to reproduce:

• Load UIFeedback in screenshot mode by #screenshot.
• Click on "Feedback" button

-> "Feedback" dialog occurs.

• Click on the close button in the right top corner.

-> Dialog closes.

• Click somewhere in the text.

-> The whole text gets selected.

This behavior occurs in Mozilla Firefox.
This behavior occurs not in Google Chrome.

To allow drawing before the screenshot the selection gets disabled by
user-select: none
That is correct.

After closing the selection should set back to normal mode. This is done by
user-select: all
That is wrong. The default value is
user-select: text
http://www.w3.org/TR/2000/WD-css3-userint-20000216#user-select
https://developer.mozilla.org/en-US/docs/Web/CSS/user-select

Webkit does not support (-webkit-)user-select: all
https://developer.apple.com/library/safari/documentation/AppleApplications/Reference/SafariCSSRef/Articles/StandardCSSProperties.html#//apple_ref/css/property/-webkit-user-select