Our web app uses right click in a few places mainly as a convenience to power users. The same functionality can be found by using visual indicators, but may take a couple more clicks.
Overall I agree with the parent comment. Right click and long-press are hard for non-power users to find/discover.
Yes. Desktop programs use it and I expect it there. On websites I generally expect my browsers normal right click menu and won't think to try right click on your web-app (especially if your web-app falls into the large number that should be simpler websites).
Most people won't even realise that a web-app can have a right click context menu (even those that use right click in their desktop programs all the time).
However, Facebook's long-press function makes sense inside an app. It's less a webapp there, and more a desktop app--even though it's interfacing with the Internet, it's presented standalone, not as a place to go within another program. You don't expect to see the browser's long-press menu in the Facebook app, because there is no browser.
As for desktop, if they're intelligent at all, they'll use a different method there. Perhaps all the new variations will be displayed side by side. Perhaps instead of only trigfering on a "long-click", it'll expand on a normal click.
Really though? What do you do in the context menu within a browser (assuming you are not a developer looking for view source/inspect element type things?) If that was not my day job I would have absolutely no use for the browser's context menu.
Correct. I do virtually nothing with it within the browser. But I don't even think about it as a possibility - so if you put functionality in the right click menu on a website/webapp I would have basically zero chance of finding it. I don't think I'm alone.
Right click on the desktop is no more discoverable, yet it's use is pervasive and it's universally understood. Discoverability isn't the only criterion for a "good UI". Frankly for something like Facebook (on which the median user spends hours a day) it's probably not even the most important one.
