According to this article (in german, http://www.golem.de/news/protonmail-paypal-blockiert-sicheres-e-mail-projekt-von-cern-und-mit-1407-107582.html) bitcoin is a payment option, however I haven't checked it personally.
Onkel Paul
Update: there's a paragraph about bitcoin on their indiegogo page:
Do you have a BitCoin (BTC) address I can donate to?
Yes, you can get our BTC details here. If you want a perk, email us your details at [email protected]!
Topic: Paypal Freezes ProtonMail Campaign Funds (Read 1641 times)
ProtonMail should really take Bitcoin. I looked for a way to contribute with BTC when day one of the ProtonMail campaign kicked off, but found nothing. Bitcoin is censorship-free and since the currency itself is a product of cryptography, it only makes sense.
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