Firefox may be preventing you from using the Post Review button based on the Privacy Protections settings you have enabled. To resolve the issue, you can follow the steps here:
- Choose the Menu (3 stacked lines) button in the top right corner of Firefox.
- Choose Settings from the Menu.
- On the left, select Privacy & Security.
- Select Standard if it is not already checked.
- Select Reload All Tabs.
After these 5 steps, you should be able to use the Post Review button without further issue.