I cannot reproduce this using Stratini Super 3.06 + Toolbar Buttons v1.0 add-on + AIOS 0.7.18 on WinXP or Win7. Are you using same versions?
Could you remove CTB, restart Firefox and reinstall CTB?
Could you export your AIOS settings and paste them here?
Could you disable your Stylish script?
Could you disable Toolbar Buttons v1.0 add-on?
Are you pointing on any toolbar images inside CTB add-on?
Is your downloads button/indicator on the sidebar? This is the only button I changed 1px in size on this update.
Is the bug gone, if you update to Fx 20 beta 2 or install Fx 19.0.1?
Edit: removed testbuild link. Not needed anymore.