fix(ktableview): make header non-sticky in firefox (#2649)

Author: portikM

src/styles/mixins/_tables.scss

@@ -72,6 +72,10 @@
           top: 0;
           z-index: 2;
 
+          @-moz-document url-prefix() {
+            position: unset; // make header non-sticky in Firefox because otherwise tooltips are cut off by the table boundaries
+          }
+
           &.is-scrolled {
             background-color: var(--kui-color-background, $kui-color-background);
           }