Fix for selected toolbar buttons in Firefox

See https://github.com/Jermolene/TiddlyWiki5/issues/1599

themes/tiddlywiki/snowwhite/base.tid

@@ -38,8 +38,8 @@ tags: [[$:/tags/Stylesheet]]
 	<<transition "fill 150ms ease-in-out">>
 }
 
-.tc-tiddler-controls button.tc-selected svg,
-.tc-page-controls button.tc-selected svg  {
+.tc-tiddler-controls button.tc-selected,
+.tc-page-controls button.tc-selected {
 	<<filter "drop-shadow(0px -1px 2px rgba(0,0,0,0.25))">>
 }