have you added any ad blocking software recently?
one (admittedly annoying) thing to try is a fresh download of Firefox or Chrome, install just the extension, and see if that works.
barring that, I can try and see what our resident greasemonkey expert has to say. Sadly, he's exceptionally busy these days, so it may take some time.
To recap, your problem is that you cannot see the "send to BB-training" button on the "Training" page. Right?
And this problem just started today, or has been happening longer?
What's your browser, version, and OS?