ThanksAppears to be a 'feature' of Firefox.
The proposed fix, may or may not work correctly. It did for the previous test post but not this post, I had to edit it to fix the post.
Open a new tab. Type about:config in the address bar. Click through security warning if it appears.
Search for the value editor.use_div_for_default_newlines
Change the value of this entry to false
and spacing in posts should be normal and not double spaced.
My post was done that way on purpose. It's not a fault.Mine is set to true and I'm not seeing that problem on my end. Also the last 2 posts you guys made were double spaced, but not the test post Blynx. Very strange.