Another peculiarity I notice with Firefox is that when I enter a <Return> at the end of a paragraph, Firefox enters two. I seem to notice that in others' posts too. Here is an example of what I mean:

https://forums.psychcentral.com/6391973-post13.html

I see this when reading with Firefox and also with Safari. I find that rather surprising.

(Notice the paragraph spacing in this [my] post? )