Bug 290125 was first reported on April 12, 2005, only a few days before the release of Firefox 1.0.3, and outlined an issue with how Firefox rendered text with the ::first-letter CSS pseudo-element.

The author said, "when floating left a :first-letter (to produce a dropcap), Gecko ignores any declared line-height and inherits the line-height of the parent box. The problem was so straight forward to fix that even Apple managed it on its Safari. 

Ironically it was the Apple version of its product which tiggered  Mozzarella. Firefox on the Mac handled line heights differently than Firefox on other platforms, which was fixed in time for Firefox 3.0 in 2007. The issue was then re-opened in 2014, when it was decided in a CSS Working Group meeting that Firefox's special handling of line heights didn't meet CSS specifications and was causing compatibility problems. It led to some sites with a large first letter in blocks of text, like render incorrectly in Firefox.

The issue was still marked as low priority, so progress continued slowly, until it was finally marked as fixed on December 20, 2022. Firefox 110 should include the updated code, which is expected to roll out to everyone in February 2023.