Olá

Experimenta restaurar o Firefox. Aqui

Abra uma nova aba do firefox; no endereço da url, digite: about:config; clique no botão "serei cuidadoso, prometo!"; na caixa Localizar, digite: undo; aparecerá browser.sessionstore.max_tabs_undo e browser.sessionstore.max_windows_undo; altere os valores para 10.

In case you are using "Clear history when Firefox closes":

• do not clear the Browsing History

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords.

Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"

Perfeito, JMartins, solucionou o problema!

Obrigado pela valiosa dica e um ótimo fim de semana!

Obrigado JMartis, estava com o mesmo problema aqui... agora resolvido