Free Download Manager which installs FDM plugin in Firefox will be automatically disabled by Firefox once new version is released. The rapid release cycle not helping FDM plugin to compatible with newly released Firefox versions, till now whenever new versions of Firefox are released geek users able to edit install.rdf file to make Free Download Manager plugin to compatible with Firefox. Hope no more workarounds like these needed in future for FDM users as Mozilla finally reviewed FDM plugin and is now available for download in AMO. So from now onwards Firefox may not disable FDM plugin since it has been approved and supports up to Firefox v18, and from now onwards Firefox takes care of auto updating this add-on.
Free Download Manager Plugin for Firefox now available in AMO
If you’re using FDM 3.9 build 1249 on your computer, then Firefox might have disabled FDM plugin, remove that plugin and download and install the latest plugin with version number 18.104.22.168 from AMO here.