While I am not an expert with about:config, you can do it in Windows for all the applications: http://www.howto-connect.com/change-icons-and-text-size-on-windows-10/

Thank you for using Firefox!

yeah, that doesnt really do it for me. I want to change the icons separately from my system settings. its just difficult when on touch screen.

Hi there!

I understand this may not be ideal for you. Have you tried using the Density setting in the Customize window? You can find instructions on getting to the Customize window here: https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

I hope this helps.

Yes I tried it. Its good, makes the rest of the buttons large enough but the bookmarks bar is still a little small. I was hoping I could make it a little bigger.

Go to your Profile folder. Create chrome subfolder inside. There create userChrome.css with the following content:

toolbarbutton.bookmark-item
{
 font-size:15px !important;
}

TyDraniu said

Go to your Profile folder. Create chrome subfolder inside. There create userChrome.css with the following content: toolbarbutton.bookmark-item { font-size:15px !important; }

That worked great! Thank you