Ah, yeah, you're correct. Firefox had changed the permissions for this some time ago.
You can optionally toggle the browser.tabs.loadDivertedInBackground value in about:config to true, then the v shortcut will open in background.
That said, I find the add-on a must-have. I'm always using it to save web pages. Do not forget to check the HTTPS option in setting, though.
As a reference [1]:
browser.tabs.loadInBackground => when you open a regular link in a new tab using Ctrl+click (or right-click > Open in a New Tab)
default = true, do not make the new tab active
In the Options dialog/page, this is controlled by the "When I open a link in a new tab, switch to it immediately" setting.
browser.tabs.loadDivertedInBackground => when you divert a script-generated new window to a new tab using Ctrl+click, or when a page uses the target attribute to launch a link in a new window and you divert it to a new tab
default = false, make the new tab active
browser.tabs.loadBookmarksInBackground => when you load a bookmark in a new tab using Ctrl+click (or right-click > Open in a New Tab)
default = false, make the new tab active
