Extension doesn't allow for 12-words seed if words are entered 1 by 1.

[MaudSimon]

It seems the extension wallets (at least on Firefox) doesn't allow users to manually input (as in typing 1 by 1) 12 words seed when importing an existing wallet. However, if the user copy paste the 12 words directly, it works.
It seems to be a known issue.

This is the user report that triggered this issue creation:

The user created a wallet with the Chrome extension (so 12 words) and wanted to import it to the Firefox Extension. He said that when he manually entered his 12 words one by one, the Firefox extension did not accept them BUT when he copy pasted the 12 words directly (not one by one) it did.
He is sure he didn't make any typo when typing the 12 words one by one manually, he tried several times.

[MaudSimon]

@h0ngcha0 ping on this as we got more reports recently.