fix back icon in Firefox

- remove problematic defs from SVG

src/img/back.svg

@@ -13,27 +13,11 @@
  height="100"
  viewBox="0 0 100 100"
  version="1.1"
- id="svg1087"
  inkscape:version="0.92.2 (5c3e80d, 2017-08-06)"
  sodipodi:docname="back.svg"
  enable-background="new">
-<title
- id="title1642">Left arrow</title>
-<defs
- id="defs1081">
-<filter
- inkscape:collect="always"
- style="color-interpolation-filters:sRGB"
- id="filter1451">
-<feBlend
- inkscape:collect="always"
- mode="screen"
- in2="BackgroundImage"
- id="feBlend1453" />
-</filter>
-</defs>
+<title>Left arrow</title>
 <sodipodi:namedview
- id="base"
  pagecolor="#ffffff"
  bordercolor="#666666"
  borderopacity="1.0"
@@ -56,8 +40,7 @@
  inkscape:window-y="41"
  inkscape:window-maximized="1"
  scale-x="1" />
-<metadata
- id="metadata1084">
+<metadata>
 <rdf:RDF>
 <cc:Work
  rdf:about="">
@@ -96,15 +79,8 @@
 </rdf:RDF>
 </metadata>
 <g
- inkscape:label="Layer 1"
- inkscape:groupmode="layer"
- id="layer1"
- transform="translate(-3.926492e-7,-270.54187)"
- style="filter:url(#filter1451)">
+ transform="translate(-3.926492e-7,-270.54187)">
 <path
- style="color:#000000;font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:medium;line-height:normal;font-family:sans-serif;font-variant-ligatures:normal;font-variant-position:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-alternates:normal;font-feature-settings:normal;text-indent:0;text-align:start;text-decoration:none;text-decoration-line:none;text-decoration-style:solid;text-decoration-color:#000000;letter-spacing:normal;word-spacing:normal;text-transform:none;writing-mode:lr-tb;direction:ltr;text-orientation:mixed;dominant-baseline:auto;baseline-shift:baseline;text-anchor:start;white-space:normal;shape-padding:0;clip-rule:nonzero;display:inline;overflow:visible;visibility:visible;opacity:1;isolation:auto;mix-blend-mode:normal;color-interpolation:sRGB;color-interpolation-filters:linearRGB;solid-color:#000000;solid-opacity:1;vector-effect:none;fill:#222222;fill-opacity:1;fill-rule:nonzero;stroke:none;stroke-width:2.11666656;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1;color-rendering:auto;image-rendering:auto;shape-rendering:auto;text-rendering:auto;enable-background:accumulate"
- d="m 50.000978,280.44162 -40.1010516,40.10025 40.1010516,40.10025 5.6556,-5.65551 -30.434757,-30.44194 h 64.878253 v -8.0056 H 25.221821 l 30.434757,-30.44001 z"
- id="path1062"
- inkscape:connector-curvature="0" />
+ d="m 50.000978,280.44162 -40.1010516,40.10025 40.1010516,40.10025 5.6556,-5.65551 -30.434757,-30.44194 h 64.878253 v -8.0056 H 25.221821 l 30.434757,-30.44001 z" />
 </g>
 </svg>