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Install thunderbird-38.6.0-1.fc23.x86_64 Install Theme Font & Size Changer 44.2 Expected: - Menus show up for Theme Font & Size Changer. Observed: - No menus appear for the add-on. Downgrade to thunderbird-38.3.0-1.fc23.x86_64 still doesn't fix it. Upstream claim is "This extension supplies customization which should be part of Firefox and Thunderbird by default! Works like a charm. However, the latest version (44.2 as of this writing) does not work in Firefox 44.0.2 or Thunderbird 38.5.1 in Linux. No toolbar icon or ability to change settings is available in either. Had to roll back to extension 43.10, which (still) works perfectly, and disable automatic updates." https://addons.mozilla.org/en-US/thunderbird/addon/theme-font-size-changer/ Filling this just in case something changed on the thunderbird side of the equation, or a known workaround exists.
Confirmed 43.3 Theme Font & Size Changer works with thunderbird-38.6.0-1.fc23.x86_64 https://addons.mozilla.org/en-US/thunderbird/addon/theme-font-size-changer/versions/?page=1#version-43.3
Okay, Thanks for the info.