Firefox not affected by gtk theme

Solution 1:

You can use Gnome Tweak Tool to use the dark theme for all the applications:

tweak tool - enable dark theme for all applications

BUT

Firefox uses GTK2. Gnome Tweak Tool only edits the GTK3 settings, hence we need to edit the /usr/share/themes/Adwaita/gtk-2.0/gtkrc file.

  1. Initially we backup our gtkrc file

    sudo cp /usr/share/themes/Adwaita/gtk-2.0/gtkrc /usr/share/themes/Adwaita/gtk-2.0/gtkrc.bak
    
  2. Next copy the following and replace your existing gtkrc file:

    #Color scheme originally contributed by Franco Gotusso as Clearlooks-DarkOrange 
    # Based on Clearlooks-DarkCoffee by Chibi and edited by bvc as Clearlooks-DarkCoffee2
    
    style "clearlooks-default"
    {
      GtkMenuItem::selected_shadow_type = none
      GtkWidget::interior_focus = 1
      GtkButton::default_border = { 3, 3, 3, 3 }
      GtkButton::default_outside_border = { 3, 3, 3, 3 }
      GtkRange::trough_border = 2
    
      GtkWidget::focus_padding = 1
    
      GtkPaned::handle_size = 6
    
      GtkRange::slider_width = 15
      GtkRange::stepper_size = 15
      GtkScrollbar::min_slider_length = 30
      GtkCheckButton::indicator_size = 12
      GtkMenuBar::internal-padding = 0
    
      GtkTreeView::expander_size = 14
      GtkExpander::expander_size = 16
    
      GtkTreeView::odd_row_color = "#404040"
    
      GtkWidget::cursor_color           = "#72706E"
      GtkWidget::secondary_cursor_color = "#72706E"
    
      xthickness = 1
      ythickness = 1
    
      fg[NORMAL]        = "#d2cfcc" #Main window text
      fg[PRELIGHT]      = "#E9E9E9" #Highlighted widget text
      fg[ACTIVE]        = "#ADA59D" #Inactive widget text
      fg[SELECTED]      = "#E9E9E9"
      fg[INSENSITIVE]   = "#A18989"
    
      bg[NORMAL]        = "#393f3f" #Backround
      bg[PRELIGHT]      = "#3465A4" #Highlight Widget
      bg[ACTIVE]        = "#2E3232" #Selected Widget
      bg[SELECTED]      = "#3465A4" #The box words are usually in
      bg[INSENSITIVE]   = "#282B2B" #Not active buttons
      base[NORMAL]      = "#4F524F" #Text area widgets
      base[PRELIGHT]    = "#313131" #Check and radio button background
      base[ACTIVE]      = "#313636" #Unfocused Select
      base[SELECTED]    = "#2F4C6D" #Selected Text area item, and that bar over the tabs.
      base[INSENSITIVE] = "#f5f2ee" #
    
      text[NORMAL]      = "#EEEEEC" #Text area widget text.
      text[PRELIGHT]    = "#E9E9E9" #
      text[ACTIVE]      = "#ADA59D" #
      text[SELECTED]    = "#E9E9E9" #Selected Text area widget text.
      text[INSENSITIVE] = "#757575" #
    
    engine "clearlooks"
       {
        #    sunkenmenubar      = 1       # 0 = disable, 1 = enable
        #    menuitemstyle      = 1       # 0 = flat, 1 = 3d-ish (button)
        #    listviewitemstyle  = 1       # 0 = flat, 1 = 3d-ish (gradient)
        #    progressbarstyle   = 0       # 0 = candy bar, 1 = flat
      }
    }
    
    style "clearlooks-wide" = "clearlooks-default"
    {
      xthickness = 2
      ythickness = 2
      bg[NORMAL]   = "#414141"
      bg[PRELIGHT] = "#494949"
    }
    
    style "clearlooks-button" = "clearlooks-wide"
    {
      bg[NORMAL]   = "#414141"
      bg[PRELIGHT] = "#494949"
    }
    
    style "clearlooks-notebook" = "clearlooks-wide"
    {
      bg[NORMAL] = "#404040"
      bg[ACTIVE] = "#303030"
    }
    
    style "clearlooks-tasklist" = "clearlooks-default"
    {
      xthickness = 5
      ythickness = 3
    }
    
    style "clearlooks-menu" = "clearlooks-default"
    {
      xthickness = 2
      ythickness = 1
      bg[NORMAL] = "#404040"
    }
    
    style "clearlooks-menu-item" = "clearlooks-default"
    {
      xthickness = 2
      ythickness = 3
      fg[PRELIGHT]   = "#E9E9E9"
      text[PRELIGHT] = "#E9E9E9"
      base[PRELIGHT] = "#3465A4"
      base[SELECTED] = "#3465A4"
    }
    
    style "clearlooks-menu-itembar" = "clearlooks-default"
    {
      xthickness = 3
      ythickness = 3
    }
    
    style "clearlooks-tree" = "clearlooks-default"
    {
      xthickness = 2
      ythickness = 2
    }
    
    style "clearlooks-frame-title" = "clearlooks-default"
    {
      fg[NORMAL] = "#e2dfdc"
    }
    
    style "clearlooks-panel" = "clearlooks-default"
    {
      xthickness = 3
      ythickness = 3
    }
    
    style "clearlooks-tooltips" = "clearlooks-default"
    {
      xthickness = 4
      ythickness = 4
      bg[NORMAL] = "#3465A4"
    }
    
    style "clearlooks-progressbar"  = "clearlooks-default"
    {
      xthickness = 1
      ythickness = 1
       fg[PRELIGHT]         = "#e2dfdc"
       bg[NORMAL]           = "#2d1d11"
    }
    
    style "clearlooks-combo" = "clearlooks-default"
    {
      xthickness = 1
      ythickness = 2
      fg[NORMAL]            = "#141414"
      fg[PRELIGHT]          = "#ed7013"
      fg[ACTIVE]            = "#e2dfdc"
      bg[NORMAL]            = "#414141"
      bg[PRELIGHT]          = "#494949"
    }
    
    style "clearlooks-scrollbar" = "clearlooks-default"
    {
      fg[NORMAL]            = "#141414"
      fg[PRELIGHT]          = "#e2dfdc"
      fg[ACTIVE]            = "#e2dfdc"
      bg[NORMAL]            = "#414141"
      bg[PRELIGHT]          = "#494949"
    }
    
    style "clearlooks-spin" = "clearlooks-wide"
    {
      fg[NORMAL]            = "#141414"
      fg[PRELIGHT]          = "#e2dfdc"
      fg[ACTIVE]            = "#e2dfdc"
      bg[PRELIGHT]          = "#414141"
      bg[ACTIVE]            = "#494949"
    }
    
    class "GtkWidget" style "clearlooks-default"
    class "GtkRange" style "clearlooks-wide"
    class "GtkFrame" style "clearlooks-wide"
    class "GtkSpinButton" style "clearlooks-spin"
    class "GtkStatusbar" style "clearlooks-wide"
    class "GtkMenu" style "clearlooks-menu"
    class "GtkMenuItem" style "clearlooks-menu-item"
    widget_class "*MenuItem.*" style "clearlooks-menu-item"
    class "GtkEntry" style "clearlooks-wide"
    widget_class "*.tooltips.*.GtkToggleButton" style "clearlooks-tasklist"
    widget_class "*.GtkTreeView.GtkButton" style "clearlooks-tree"
    widget_class "*.GtkCTree.GtkButton" style "clearlooks-tree"
    widget_class "*.GtkList.GtkButton" style "clearlooks-tree"
    widget_class "*.GtkCList.GtkButton" style "clearlooks-tree"
    widget_class "*.GtkFrame.GtkLabel" style "clearlooks-frame-title"
    widget_class "BasePWidget.GtkEventBox.GtkTable.GtkFrame" style "clearlooks-panel"
    widget "gtk-tooltips" style "clearlooks-tooltips"
    class "GtkNotebook" style "clearlooks-notebook"
    class "GtkProgressBar" style "clearlooks-progressbar"
    widget_class "*.GtkComboBox.GtkButton" style "clearlooks-combo"
    widget_class "*.GtkCombo.GtkButton" style "clearlooks-combo"
    class "GtkButton" style "clearlooks-button"
    class "GtkScrollbar" style "clearlooks-scrollbar"
    

Solution 2:

On newer Firefox versions (67) GTK3 dark theme support is still rubbish. (Form widgets often render with wrong colors.) Here's a band-aid fix:

Goto: about:config 
Add String entry: widget.content.gtk-theme-override
Set value to: Adwaita:light
Goto Customizations: choose Dark theme