Odd - it worked for the bold and italic text in your earlier post.
It makes no difference whether BBCode tags are typed manually or added to selected text via a button-press because the end result is the same: an opening and closing attribute tag bracketing some text.
If the tags are mismatched or mistyped in some way then they become visible instead of silently applying the attribute, but that's not what happened above - the tags are fine and the attribute is displayed correctly.
Do these attributes all appear for you?
This is bold, italic, bold and underlined, italic and underlined.
Red text, green text, blue text.
If not, do you see the "[xxx]" tags themselves or just plain unadorned text with no attributes or tags?
When previewing your own posts do you see the tags instead of the attributes they're supposed to add?
Selecting the "Disable BBCode in this post" option at the foot of the post edit window will leave the tags intact but prevents them from applying an attribute, with the result that they appear as plain text along with the post body - but you don't have that selected as a default in your profile so it would need to be actively selected when posting (and I think you'd notice doing that ).
The application of an attribute is carried out by the forum software using html, so any browser except a plain text browser such as Lynx should be capable of decoding and rendering it for this site in the same way as it would for any others.
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Giraffe: a ruminant with a view.