use back-to-top initializer, fixes #2840

app/assets/javascripts/diaspora.js

@@ -59,6 +59,7 @@
   Diaspora.BasePage = function(body) {
     $.extend(this, Diaspora.BaseWidget);
     $.extend(this, {
+      backToTop: this.instantiate("BackToTop", body.find("#back-to-top")),
       directionDetector: this.instantiate("DirectionDetector"),
       events: function() { return Diaspora.page.eventsContainer.data("events"); },
       flashMessages: this.instantiate("FlashMessages"),

app/assets/javascripts/widgets/back-to-top.js

@@ -11,7 +11,7 @@
 
       self.button.click(self.backToTop);
 
-      var throttledScroll = _.throttle($.proxy(self.throttledScroll, self), 250);
+      var throttledScroll = _.throttle($.proxy(self.toggleVisibility, self), 250);
       self.window.scroll(throttledScroll);
     });
 

app/assets/stylesheets/application.css.sass

@@ -2850,7 +2850,7 @@ a.toggle_selector
   :background-color #aaa
   &:hover
     :opacity 0.85 !important
-  &:visible
+  &.visible
     :opacity 0.5
 
 .float-right