Fix this issue by removing all data stored in Firefox for a specific domain, i.e. Gmail, by selecting “Forget About This Site”. Click on the menu icon to choose History from the list. Next, click on Show All History to open a list of all data, including cache, cookies, and History. Click on View next and then on the sidebar. Finally, fix Gmail not working on Firefox, click on History and then on Forget About this site. This action will remove all site’s temporary data.

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