Hello there,

The confirmation email can take a few minutes to get to your inbox. Spam filters might also prevent it from reaching the right folder. If you've already waited a few minutes and refreshed your inbox, try the following steps:

1) Check your junk mail or spam folder to see if your confirmation email ended up there. 2) Click the Resend email link on the Firefox Sync signup page. 3) If you still don't see the confirmation email after trying the preceding steps, a strong spam filter might have prevented the confirmation email from reaching you at all. Try adding accounts.firefox.com to your list of allowed senders to keep your email provider from blocking the email.

Hope this helps.

Unfortunately, it doesn't help. I have already tried all these solutions and failed to achieve any results.

Additional info, maybe it matters: I am not trying to set up a new account, I logged in with an existing account on a new device and then Sync requested verification for safety reasons. But I got no verification e-mail and now Sync doesn't work for me on any device (I tried sending verification e-mail from different devices and got nothing). This guy - https://support.mozilla.org/pl/questions/1049903 - solved similar problem by setting up an account through firefox on android, but I own windows phone, so bad luck for me.