Hi,
Well that was an interesting list of problems to figure out and glad you all saved them up but i think i have fixed most of them if not all.
Many come back to the use of the WYSIWYG Editor option and things seem to behave a lot better when I switched it off so I turned it off for everyone...I Think. If you are still having any issues as described earlier, go into to your profile and under Forum Settings-> Look and Layout make sure the 'Use WYSIWYG' is not ticked and if it is, un-tick it and try again.
The above was definitely the cause for the 'Double Spacing' between line paragraphs and and wasn't helping the FireFox dictionary issue. I couldn't recreate the 'Font and Size' BBC code issue but it is most likely the culprit there too.
FireFox users using the spell checker might find that you need to turn the spell checker on again so you can do that in Tools->Options or Right Click in the Post/Reply box and then select Check Spelling and re-try. There seems to be two issues, one with FireFox and one with SMF(the Forum Software) and if both planets are aligned it falls off, no fix in sight from either so you might need to remember the above.
Now I did find something handy in chasing down this problem and that is an Australian Dictionary,
https://addons.mozilla.org/en-US/firefox/addon/english-australian-dictionary/ , which you can install as an add-on to Foxy and then using the same right click as above, under Check Spelling is
Languages and then under that select the Aussie one. You do need to restart the browser after installing the add on before it will show up under Languages.
Right-Click for Pasting seems to work fine in Fox and Chrome and there was a post I read somewhere suggesting it wasn't working in FF 11.
Don't have Safari or an iSplat to see what is going on with the formatting of the Avatars so need pictures next time you see it happen but i couldn't see any options to tweak for that so i suspect it is html rendering related.
Almost a waste of a good few hours of my life but did learn stuff along the way.
Terry