It appears that Firefox on Windows shows accents that have not been normalized according to the Unicode Normalization Form C to the right of the character. In some cases the accent is still over the correct character, in other cases it is completely over the next character to the right.

Next to symbols with an accent "included", for example é, one can take the symbol without accent and add the accent afterwards, like é. You shouldn't be able to see a difference, but I find that in some cases I do. The Open Library webpage linked with this report renders normally in Firefox on a Mac, but on Windows the accents in the author's name float to the right and are visibly disconnected from the letters. The font used for the name on the website is Trebuchet MS, but the same font with the same text in LibreOffice renders just fine.