Menu (Alt/F10) File > Offline and uncheck "Work Offline". You can also configure TB to always start online, by going to the menu Tools > Options > Advanced > Network & Disk Space > Offline and uncheck " Automatically follow detected online state" and select "Online".

This person has been repeated asking the same question and not providing any feedback.

So trying to het them to keep to the following: https://support.mozilla.org/en-US/questions/1179234

@bbonne, you have asked the same question three times in less than 24 hours. Please refrain from duplicate requests. It is not only confusing but wastes the time of volunteers trying to assist you. You now have responses from three individuals that probable help you little because they are all looking at the problem from slightly different angles.

Based on the details and conversations I am going to designate https://support.mozilla.org/en-US/questions/1179237 as the canonical topic and lock the duplicate questions.

https://support.mozilla.org/en-US/questions/1179234 and https://support.mozilla.org/en-US/questions/1179231 Will be locked. Please continue the discussion in the canonical thread.