This is true in both IE and FF:

I double click on a word to highlight it - and the space after the word always gets highlighted too.

I have to click and drag to get the word without the space.

Why is this?

Can I fix it?

You can double click then hold shift and hit the left arrow. This will select the whole word... though not perfect I agree.

I don't think you can fix it because it's how it's meant to work :/

Maybe Firefox extensions? :)

Apparently it's hotwired into MSHTML

See http://blogjet.com/forum/viewtopic.php?pid=202