After updating Firefox for Linux, the folder icons in the bookmarks menu disappeared

Only a short post this time, but this problem has been annoying me for a few weeks. I use KDE 4.14 (kde-meta-4.14.3-r1) in Gentoo Linux on my main laptop, and recently upgraded Firefox to Version 46.0. The folder icons in Firefox’s bookmarks menu were no longer visible, although favicons were still visible in the bookmarks menu. The 2011 mozillaZine Forums thread After updating- ff4 bookmark folder icons disappeared [Linux] steered me in the right direction: I checked KDE 4’s ‘System Settings’ > ‘Application Appearance’ > ‘GTK’ and found that ‘Show icons in GTK menus’ was not ticked. I ticked this and clicked on ‘Apply’, and the problem was solved.