I'm having a similar problem with OW and Yahoo Mail (the new beta version) Yahoo Mail does not let me use the new mail with OW as OW but I can use the beta version identifying as Firefox. All goes well until I try to delete bulk mail. It behaves as if it has deleted it but then a notice comes up of "incorrect version." The next time that Yahoo Mail refreshes the bulk mail is back again.
I have tried various combinations of ad blocking and cookies in the site preferences to no avail. BTW Firefox itself does not have this problem with the new Yahoo Mail
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