Danke für Eure Antworten,
ich arbeite immer online.
Bis jetzt komme ich zu folgendem Schluss: auf allen Rechnern, an denen ich online immer per typo3 an der Webseite arbeite, interpretiert der IE 11 die media queries korrekt und auf allen anderen PC tut er das überhaupt nicht....
Aber das kann doch nicht sein.

Ich füge mal die queries hinzu - vielleicht findet Ihr ja irgendwelche Fehler, die ich übersehen habe?!?!!?

Ich sage schon mal DANKE! Adlerauge

/*********************************************/
/* Bildschirm, normal (devices and browsers) */
/*Breite: 961px - unendlich*/
@media all and (min-width: 961px)             {

.slider_first {height:320px;}

} /*/

/***************************************************************/
/* Tablet Portrait size to standard 960 (devices and browsers) */
/*Breite: 771px - 960px*/

@media all and (min-width: 771px)           {

.slider_first {height:none;}

}/*/

/************************************************************************/
/* Mobile Landscape Size to Tablet Portrait (devices and browsers) */
/* width: 481-770px*/

@media all and (min-width: 481px) and (max-width: 770px)  {

.slider_first {height:none;}

img, embed, object, video {max-width: 100%; height: auto; height: 50%; overflow:hidden; width: auto; width:100%;}
*html img {width: auto; /* IE8 */}

.col_66, .col_50, .col_33, .col_25 {float:none; width:98%; margin:0 auto 0 auto; padding:1%;}

.content, .header-top, .footer, .mainmenu {min-width:481px; max-width:770px; width:100%; padding:0; margin:0;}

.title, .title h1 {float:none; display:block;}

/*text und bild; float aufheben*/
.csc-textpic-imagewrap, .csc-textpic-image {float:none; width:100%;}
.csc-textpic-image a img, .csc-textpic-image img {max-width: 100%; height: auto; width: auto;}
.csc-textpic-text {display:block; width:100%; }

/*text und bild; float aufheben*/
.csc-textpic-imagewrap {float:none;}
.csc-textpic-image a img, .csc-textpic-image img {width:100%;}
.csc-textpic-text {display:block; width:100%; }

} /*Klammer: Ende 481-770*/

/************************************************************************/
/* Mobile Portrait Size to Mobile Landscape Size (devices and browsers) */
/* Width:321-480px*/

@media all
and (min-width: 321px)
and (max-width: 480px)                  {

/*Header_top und slider nicht mehr fixed--> keine PlatzProbleme mit nachfolgenden Inhalten*/
.header_top {position:relative; margin-bottom:0;}
.bce_logo {padding:0;}
.bce_logo img {width:100%, height:auto;}
.slider_first {overflow:hidden; width:100%; padding:0; height:none;}

img, embed, object, video {max-width: 100%; height: auto; height: 50%; overflow:hidden; width: auto; width:100%;}
*html img {width: auto; /* IE8 */}

.col_66, .col_50, .col_33, .col_25 {float:none; width:98%; margin:0 auto 0 auto; padding:1%;}

.content, .header-top, .footer, .mainmenu {min-width:321px; max-width:480px; width:100%; padding:0; margin:0;}

/*mainnavi*/
ul.menu {margin:0 auto; box-shadow:none;}
ul.menu li {float:none; margin:0 auto; text-align:center; box-shadow:none;box-shadow:none;}

.mainmenu ul.menu, .mainmenu ul.menu ul {list-style-type: none; }
.mainmenu ul.menu {padding:0; margin:0; text-align:center; box-shadow:none; }
ul.menu a {
  display: block;
  padding: 0.1em 0;
  font-weight:normal;
  text-decoration:none;}

ul.menu ul a {padding: 0.1em 0;}
ul.menu ul li a {font-size:1em;} /*16px*/
ul.menu li {
    padding:0 0 0;
    margin:0;
    background-image: none;
    float:none;
    display:block;
    background-color:silver;
    box-shadow:none;
 }

ul.menu ul {
  margin:0;
  margin-left:0;
    padding:0;
    position: relative;
    display:block;
    background-color:#fff;
    min-width:100%;
    z-index:10;
    clear:both;
    display:none;
    box-shadow:none;
}

/*aufgeklapptes Untermenu HOVER*/
ul.menu ul li:hover {display:inline-block; box-shadow:none; background:none;}

ul.menu ul li a {
  display:block;
  font-size:70%;
  padding: 0.3em;
  font-weight:normal;
  text-decoration:none;
  border:0;
  shadow:none;
  background:none;}

/*a normal und ACTIVE*/
ul.menu li a {text-transform:none;}
ul.menu li a:hover, ul.menu li a.active {color:#666; border:none;  background:none;}

.rounded_top {border:none; box-shadow:none;}

/*text und bild; float aufheben*/
.csc-textpic-imagewrap, .csc-textpic-image {float:none; width:100%; }
.csc-textpic-image a img, .csc-textpic-image img {max-width: 100%; height: auto; width: auto;}
.csc-textpic-text {display:block; width:100%; }

/*text und bild; float aufheben*/
.csc-textpic-imagewrap {float:none;}
.csc-textpic-image a img, .csc-textpic-image img {width:100%;}
.csc-textpic-text {display:block; width:100%; }

} /*Klammer: Ende 321-480px*/

/************************************************************************/
/* Mobile Portrait Size to Mobile portrait Size (devices and browsers) */
/* Width:320px*/

@media all
and (max-width: 320px)         {

/*Header_top nicht mehr fixed--> keine PlatzProbleme mit nachfolgenden Inhalten*/
.header_top {position:relative; margin-bottom:0;}
.bce_logo {padding:0;}
.bce_logo img {width:100%, height:auto;}
.slider_first {overflow:hidden; width:100%; padding:0; height:none;}

img, embed, object, video {max-width: 100%; height: auto; height: 50%; overflow:hidden; width: auto; width:100%;}
*html img {width: auto; /* IE8 */}

.col_66, .col_50, .col_33, .col_25 {float:none; width:98%; margin:0 auto 0 auto; padding:1%;}

.content, .header-top, .footer, .mainmenu {max-width:320px; width:100%; padding:0; margin:0;}

.header-top, .footer {display:none;}

/*mainnavi*/
ul.menu {margin:0 auto;}
ul.menu li {float:none; margin:0 auto; text-align:center;}

/*text und bild; float aufheben*/
.csc-textpic-imagewrap, .csc-textpic-image {float:none; width:100%; }
.csc-textpic-image a img, .csc-textpic-image img {max-width: 100%; height: auto; width: auto;}
.csc-textpic-text {display:block; width:100%;}

/*text und bild; float aufheben*/
.csc-textpic-imagewrap {float:none;}
.csc-textpic-image a img, .csc-textpic-image img {width:100%;}
.csc-textpic-text {display:block; width:100%;}

} /*Klammer: bis 320px*/

/************************************************************************/
/* highres devices */
@media all and (-moz-min-device-pixel-ratio:1.5),
  screen and (-o-min-device-pixel-ratio:3/2),
  screen and (-webkit-min-device-pixel-ratio:1.5),
  screen and (min-device-pixel-ratio:1.5){}