This is very annoying and also hard for web developers who want to see how things look on Android. You may be fooled into thinking you have an unclosed bracket or incompatible code but this is the "text inflation feature" which I feel should be disabled by default. It works so inconsitently that one block of text will appear small while the other will be huge and is quite annoying.
The solution is simple
Settings -> Display and "Text Size" (set it to tiny) or make the text as small as it can be until won't go smaller and hit "Set" to disable it. This really is not untuitive and a bit of crazy quirk and hack on the part of Mozilla.
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