Can tweak this sort of stuff with a userChrome.css or userContent.css file. Some instructions here might help.
https://www.userchrome.org/Though it seems some things need to be in userContent.css, not userChrome.css. Not sure what the differences are.
So create a userContent.css and add this.
textarea:focus{
outline:0;
}
input[type="text"]{
outline:0;
}
That should hide the outlines for text boxes anyway.