I'm currently working on a bookmark extension for Chrome, initially targeting my own needs, but I hope to make it available to others eventually. I'm wondering if there are any insights you could share about what factors led to the quality issues you mentioned.
sometimes i just outsourced stuff to people who were not technically capable enough. even good-ish devs can have trouble with the javascript event loop / promises / etc.
outside of that, i think quality can tumble when a solo dev starts to lose interest -- i.e. burnout.