About a year ago, I tried using LastPass but found the user experience very lacking, and went back to my tried-and-true method of just having a bunch of different passwords (some password reuse, but I've never ran into problems with it) and my email has a unique, non-reused passphrase of 30+ characters and I reckon I could just password reset any service eventually hijacked.
I know this is not good, and I understand the consequences - this is not about that.
I recently decided to "hey, let's give password managers another shot" and this time went with Firefox Sync (& Master Password).
From what I've noticed, it encrypts the locally stored cryptoblob using a key, which is in itself encrypted using the master password. The passwords stored on their server is (for some reason) encrypted using my Firefox Sync password (which is, of course, stored in the cryptoblob).
Full disclosure: My Firefox Sync password is not as strong as my master password. If someone stole it, they could theoretically download an unencrypted copy of my password blob to a new device simply by logging into my account. However; this requires me to confirm the login from my e-mail. The password to my email is, at current date, the same passphrase I use for my firefox master password.
Now, to the question: Is there something inherently less secure in using a long, humanly memorable passphrase (my master password) for my e-mail (which is required to download my cryptoblob) than having it be a data-secure password stored in said cryptoblob?