[Ethereum] Seed phrase of existing account in Metamask on different browser gave different address

I don't think it will look up previous transactions in the chain. Afacit the only way to do that is by looping over the blocks and I can't see any code that does that.

edit: my comment is substantiated by the issue that Nicolas linked above: https://github.com/MetaMask/metamask-plugin/issues/505 MetaMask does not implement this functionality (although other wallets might).

If you were using the Google Chrome browser in Windows 10, you should be able to find the location of the Vault by going to this folder location (you need to be able to see the hidden files):

C:\Users\USER_NAME\AppData\Local\Google\Chrome\User Data\Default\Local Extension Settings\nkbihfbeogaeaoehlefnkodbefgpgknn

In that folder you'll see a file called 000003 (or something like that), open that file with a text editor or code editor software like Atom (https://atom.io/).

In the text editor search for the word "vault" and copy this part that looks like the one pasted below:

{"vault":"{\"data\":\"wwpXXtFCqZkYsWfeEwItZjJ0Cc7mRVjG47Dqh+ztL1PiCG6Izhg+zG0mM+H2ykyjz3X0RNhAE6IVsWFZamcZ47B4sVi4SvUxrMhARm5L3yHPxr3UsyGrOXmthyVMgEGmjwlmnFCNd2nMZ2o8/sRMra8FupurqevnBv57FiYpEEs7gPpFHv6587aL44MmKD8Snv4JLFqiqmlK82Waq5F+Iv9mw2sFVAL9mgZBSgFgbWdB3TsKVB2k\",\"iv\":\"rkUQlNcGTxBE0My7a/bCXw==\",\"salt\":\"HcKyNfGzaRALRQ0DlKgcIe5Uk30iI/M//oG6w8vX8Nk=\"}"}

Remove the two parts in bold. Now use the Search and Replace feature of the editor to change all the \" to "

You would now have something like this:

{"data":"wwpXXtFCqZkYsWfeEwItZjJ0Cc7mRVjG47Dqh+ztL1PiCG6Izhg+zG0mM+H2ykyjz3X0RNhAE6IVsWFZamcZ47B4sVi4SvUxrMhARm5L3yHPxr3UsyGrOXmthyVMgEGmjwlmnFCNd2nMZ2o8/sRMra8FupurqevnBv57FiYpEEs7gPpFHv6587aL44MmKD8Snv4JLFqiqmlK82Waq5F+Iv9mw2sFVAL9mgZBSgFgbWdB3TsKVB2k","iv":"rkUQlNcGTxBE0My7a/bCXw==","salt":"HcKyNfGzaRALRQ0DlKgcIe5Uk30iI/M//oG6w8vX8Nk="}

You can now go to the Vault Decryptor https://metamask.github.io/vault-decryptor/ and paste that in the textfield there, enter the password you set for the extension when you created your MetaMask wallet. You should be able to see your seed phrase and any manually imported private key below if you click the Decrypt button.