Adobe Reader X finally enable writing annotations (comments) without having special rights / Acrobat installed.
While trying this new feature, I can see that it's enabled within the application, but somehow disabled via the browser (i.e opening a pdf file inside the browser).
My question is how can I enable comments while viewing a pdf file inside the browser?
You cannot. Except for the special case of a browser-based review initiated by Acrobat, the default comment tools in Adobe Reader X (highlight and sticky note) will only work in the standalone (desktop) instance of the application and not via the web browser plugin.
As a workaround, you can save the PDF to the local disk and then view it in standalone Adobe Reader.