No, and this is supported by the timing. PIA made the inaccurate (and now withdrawn) allegations in July. Mozilla was aware of the allegations, visited Proton in Geneva, looked into said allegations, and announced the Proton partnership in October.
Proton doesn't support Wireguard which is the protocol Mozilla wanted to use. This was a conscious decision because Wireguard is UDP only, which poses a significant problem for many Proton users which are based in countries with strict censorship and UDP VPN protocols are easier to block. Therefore, Proton's VPN focus has shifted to working on TCP based solutions which can resist DPI.
While Proton and Mozilla's VPN focuses have diverged, there is still collaborations and discussions in other areas. For example, Thunderbird is integrating Enigmail, which is based upon the OpenPGPjs library that Proton maintains.
Proton and Mozilla have similar missions, and will continue to support each other in the future.
