Just one anecdotal data point, but I am using Firefox for Mac OS, and on en.WP, the text got noticeably larger for me, even though this page said that I would see no change. Adding the recommended 13px setting to my css did not fix it. I had to adjust the text down to 98% to see a difference. FWIW.
Topic on Talk:Editing/Projects/Font size in the editing window
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