Can I ask why, when using FF on Android showing the mobile version of HN, replies appear using different font sizes? Some are tiny, some are actually readable.

Can I ask why, when using FF on Android showing the mobile version of HN, replies appear using different font sizes? Some are tiny, some are actually readable. I have to zoom/unzoom constantly to read just a thread, or switch to the desktop version, which doesn't have this issue. It's so dumb, I feel dumber just asking.