I created a custom skin based on the default skin which uses svg buttons.
On Firefox, these buttons are not available. Neither visible nor clickable. It works on all other brothers (mobile/desktop) though.
Code
<krpano>
<!-- krpano 1.19 default buttons skin -->
<!-- the container layer that contains the buttons -->
<layer name="defaultskin_buttons" bgcolor="0x000000" bgalpha=".5" bgroundedge="3" type="container" width="330" height="63" align="bottom=" y="-3" scalechildren="true" scale="1.0" keep="true">
<layer name="btn_left" x="15" y="15" url="/files/zzzz/pfeil-links-w.svg" width="30px" height="30px" ondown="set(hlookat_moveforce,-1);" onup="set(hlookat_moveforce,0);" />
<layer name="btn_right" x="55" y="15" url="/files/zzzz/pfeil-rechts-w.svg" width="30px" height="30px" ondown="set(hlookat_moveforce,+1);" onup="set(hlookat_moveforce,0);" />
<layer name="btn_up" x="95" y="15" url="/files/zzzz/pfeil-oben-w.svg" width="40px" height="30px" ondown="set(vlookat_moveforce,-1);" onup="set(vlookat_moveforce,0);" />
<layer name="btn_down" x="145" y="15" url="/files/zzzz/pfeil-unten-w.svg" width="40px" height="30px" ondown="set(vlookat_moveforce,+1);" onup="set(vlookat_moveforce,0);" />
<layer name="trennstrich" x="205" y="15" url="/files/zzzz/trennstrich-w.svg" width="10px" height="30px" />
<layer name="btn_autorot" x="235" y="15" url="/files/zzzz/drehen-aus-w.svg" width="30px" height="30px" onclick="switch(autorotate.enabled);" />
<layer name="btn_fs" x="275" y="15" url="/files/zzzz/vollbild-ein-w.svg" width="30px" height="30px" onclick="switch(fullscreen);" visible="true" devices="fullscreensupport" />
</layer>
<!-- the container layer that contains the close button -->
<layer name="defaultskin_button_close" type="container" width="30" height="30" align="righttop" y="15" x="15" scalechildren="true" scale="1.0" keep="true">
<layer name="btn_close" x="0" y="0" url="/files/zzzz/schliessen-overlay.svg" width="30px" height="30px" onclick="js(window.history.back())" visible="true" />
</layer>