Hi, Boyard
I think most of the add-ons I have in my own TB installation had to be done by downloading and installing separately. Only ccasionally, will one install immediately and be fully operative after a re-start. So, I can't speak for why the difference or why you only noticed this today.
In any case, if you're offered the download window you referred to:
1) click to 'save' and save the file to the desktop for most convenience.
2) in TB, open settings > add-ons.
3) look for a gear icon along the top right of the page. Click it and select "install add-on from file."
4) select the desktop file you just downloaded and click 'ok.'
5) when the 'install now' button shows ready, click it
6) when installation is done, restart
You should be good to go.
Hope this helps!