Firefox not affected by gtk theme
You can use Gnome Tweak Tool to use the dark theme for all the 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.
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
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"