There is no workaround possible for lost access due to 2FA.

• https://support.mozilla.org/en-US/kb/what-if-im-locked-out-two-step-authentication

You will have to create a new Firefox Account and connect all devices to that account. If you decide to enable 2FA then make sure to keep a backup of the recovery code or keep a backup of the (decoded) QR code. Start with connecting the device that has your data.

If the device with your data is a desktop device then you can also transfer data directly.

You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager
  key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db
• cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words added to the spell checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

narimantas97, just thinking that it might be best not to publish real email addresses on a public forum?

Anyway, according to the article: https://support.mozilla.org/en-US/kb/what-if-im-locked-out-two-step-authentication#w_i-lost-my-two-step-authentication-device-but-i-have-another-logged-in-device , under the heading "I lost my two-step authentication device but I have another logged-in device." it says: "If you're locked out of your account but have a device still logged in via two-factor authentication, you can use that device to disable two-factor authentication" So you could try those instructions. Hope they work for you, but it might be the case that your other synced device would need to already be fully logged in.