Looks like font.size.systemFontScale is gone in Firefox 105 and everything is smol again. There might have been a lot of incentives for removing it — breaking screenshooting feature for one, if the var vas set to anything but 100, screenshot region wasn't scaled accordingly and you got cropped screenshots or empty space around what you wanted.
Now there is ui.textScaleFactor that does the same and works, but screenshots are still skewered. What was the point then? 🤔