Leah had exclusive control of libreboot. Leah is transgender. The FSF fired someone who happened to be transgender. Leah accused the FSF of doing it because they were transgender. Leah pulled libreboot out of the FSF, burned various bridges by calling people names and retained exclusive control of libreboot, making statements in the project's name.
Apparently she changed her mind and libreboot has transitioned into a more democratic project and she's sorry for what she did and cites personal issues which the letter spells out as gender dysphoria and substance abuse.
A quick googling shows that both the FSF and Leah have mostly refrained from naming names when talking about who got fired but Leah explicitly called out individual members of the FSF (which she apologises for in the letter, indicating she no longer thinks her accusations hold any water). There are also various posts from libreboot contributors complaining about Leah having effectively locked them out of the project and apparently the entire ordeal didn't exactly result in quality software releases (which is to be expected).
tl;dr: maintainer with exclusive access has personal problems, lashes out against FSF, takes project hostage, works personal problems out over the next six months, hands control over project to the other contributors and repents.