if I write several words and click on one word, Mozilla selects the word together with the space following it. I don't want to change this, as I find it practical.
When I then click on "url", a space will be before the [/url] tag and no space after it. This has not made any problem until now, but now the space before the tag is deleted on posting or previewing (only for the url tag, not with b, i or u tags), leaving text like
one twothree

Wikipedia solves this issue by putting the tags only around the word, when clicking a button, even if a space is selected after the word. Could that be a solution?