hi, does the following addon help you to tweak the interface a bit for better visibility?: https://addons.mozilla.org/firefox/addon/theme-font-size-changer/

If that add-on doesn't do it for you, see this website: http://www.accessfirefox.org/

This is probably a good site to be aware of http://www.accessfirefox.org/Firefox_Accessibility_Extensions.php It is a semi official mozilla community run site. IIRC the site and many of its addons were caught out by Australis. That is probably one site we should reach out to in advance if for instance making anything less distinct smaller, or lower contrast.

You can look at the Classic Theme Restorer extension to customize the appearance and restore features used in older Firefox versions.

• Classic Theme Restorer: https://addons.mozilla.org/firefox/addon/classicthemerestorer/

• You can check out the settings of the CTR extension via its Options/Preferences button on the "Firefox/Tools > Add-ons > Extensions" page.
• You can find extra toolbar buttons and more toolbar settings in Customize (3-bar Firefox menu button > Customize)

You can look at the NoSquint extension to set font size (text/page zoom) and text color on web pages.

• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/