Right-click on a block = Context menu for Copy/Paste and other like this
Double-click on a block = Open the window with it's settings. There is one extra window that appears only when you have at least one Variable defined
If something does not work, it's probably because of the browser, but all modern browsers should work. Please, don't try it on some old IE... even I don't know what will be the outcome.
Firefox and Chrome works fine. I noticed some problem with the scroller in the blocks list on Chrome. I normally use Firefox because of the "Connector" plugin that makes it possible to write output files directly into the output folders. There was similar plugin for Chrome as well, but it was built on old technology and they removed that, so now it's not working and I need to find some other way.
Also, there is a desktop version that has it's own Chrome and works totally offline. It is the same thing, but wrapped into .exe file.