In version 335 notifications don't work properly. Once the notification window disappears, it disappears also the overlay number of unread notifications from Pushbullet icons.
If "Show notifications on my computer" in the settings is unchecked, overlay number of unread notifications on the icon remains, but I don't see a preview of notification at the bottom right :-)
I tried the 335 version on Firefox 50, 49 and 48 (although warning about incompatibility) and badly it behaves in all versions. I tested clean install of FF, Pushbulet was only one added addon.
Previous versions Pushbullet addon works OK, but it's not WebExtensions version, so over time the new versions of Firefox apparently stops working :-(
In the addon for Chrome and the Pushbullet desktop app too it works fine, but I prefer Firefox addon.

Please repair addon, if possible.

Many thanks, Petr F.