Classic CSS tweaks for Firefox Quantum v2.9.9

Full changelog: https://github.com/Aris-t2/CustomCSSforFx/commits/

[GENERAL]

• (general variables) lowered value of default general font size variable
• (userChrome.css) appbutton in titlebar > changed file/option names (v3)

[Appbutton]

• (new) Fx74+: own options for Firefox 74+ > removed Fx71+ workarounds (v3)
• (tweak) changed how different appbutton icon options have to be enabled (v3)

[General UI]

• (fix) findbar on top glitch

[Tabs]

• (fix) tabs below navigation toolbar + lw-themes + Win7 AeroGlass

[Add-on Manager (about:addons)]

• (tweak) Fx72+: show buttons instead of menu popup > replaced themes Enable/Disable with a checkbox/switch
• (tweak) Fx72+: show buttons instead of menu popup > theme image size
• (fix) Fx68+: alternative appearance / alternative appearance Aero > details page

[about:preferences]

• (tweak) alternative appearance options v1, v2, Aero