"the message well doesn't display anymore but job cancelation has no effect" hmmm...maybe you missed this point of the comment.
I did not. You told your browser "From now on, automatically reject all popup messages from this site", and that's what happens. Jenkins asks for confirmation, your browser tells it "No", and nothing gets cancelled. Remember, your computer does what you tell it to do, not what you want
The job cancellation has no effect and the jenkins ui is stuck, and the job will not be cancelled. I have to delete the job and/or restart jenkins.
Or, you know, restart your browser to clear the flag you accidentally set.