Support the rest of NPAPI
We're almost there but still missing a few new additions. Though some of them may not even be implemented by anyone yet.
https://wiki.mozilla.org/NPAPI:AdvancedKeyHandling https://wiki.mozilla.org/NPAPI:HTTPRedirectHandling https://wiki.mozilla.org/NPAPI:ClearSiteData
http://blog.chromium.org/2011/04/providing-transparency-and-controls-for.html
ClearSiteData may become more relevant to supporting now. This may also depend on bug #7 depending on how browsers query for support.
AdvancedKeyHandling and HTTPRedirectHandling are left. AdvancedKeyHandling has no implementation in any browser, so it can be punted for now. HTTPRedirectHandling is testable today. There's a slight bit of subtlety in the notifyData being downgraded from 64-bit to 32-bit. Would require allocating a small 64-bit object and destroying it at the appropriate point. Not impossible though.
Fixing this in the other direction (NPN_GetURLNotify) would also allow us to support 32-bit browser / 64-bit plugin. Because that use case is so important...