>>> My Info: Win7_64, Nightly 49, 32bit, ID 20160526082509 about:addons page checks the scroll height of text with release notes, and then it explicitly sets that height in CSS ('height' property). Then it shows the text block with a smooth transition. But if showing the text causes vertical overflow on about:addons page, it causes horizontal resize of the text, therefore it now has bigger height than defined in CSS property, so part of text will be invisible.