zorrotamalito: So, I have bought a documentary about Double Fine studios but from GOG Galaxy I can't watch it and from the web browser I can only download the files of the movie.
Why can't I stream it?
Actually, in recent-ish versions of Firefox, you can...as long as GOG didn't package the download as a .zip file (which they usually only do for "bonus goodies"). But for any standalone movies (and even though it's classified as a game in GOG's catalogue, I would think
Double Fine Adventure would count as such), you should just be able to click the download link and it will instead start to play it in the browser.
But, yeah, this behavior is enabled by the browser, not by GOG.