There could be many reasons for this issue but one of the most common reason is because your FDM desktop app cannot connect to the browser's FDM extension.
- Remove both the FDM desktop app and extension
- Download and install the FDM desktop app first
- After it is installed and running, install the FDM extension in the browser
- Now when you click on FDM extension icon, and then Options, it should open desktop FDM app for you which indicates that everything is well set up.
- Restart your browser just in case
(If ther is **Loading...**instead og Options in FDM extension, then that means extension is not connected to your desktop app)
- For Linux too, you could try installing and running desktop app first, then installing extension.
- Copy this file from
~/.config/google-chrome/NativeMessagingHosts/org.freedownloadmanager.fdm5.cnh.json
to~./config/.config/BraveSoftware/Brave-Browser/NativeMessagingHosts/org.freedownloadmanager.fdm5.cnh.json
for Brave browser or similarly for any other browser you're using. - Restart your browser just in case