Opera Beta 38.0, Windows 7 64bit -- if Opera is set as the default browser, OneDrive automatic (on system boot) startup (before logging in to OneDrive) consistently fails with script errors to the point where it cannot start. No opportunity to log into OneDrive is offered.

Making Microsoft Internet Explorer the default browser fixes the problem / is a workaround. The problem also does not exist if either Firefox or Google Chrome are set as the default browser.