Hi Adrian Jones,
Have you tried:
- Settings/Content area/Render feeds -> to enable/disable Drop Feeds to render (open) a Feed in a tab ?
- Settings/Content area/Always open new tab -> to enable/disable Drop Feeds to render (open) a Feed in a new tab (because you said "in another tab", I guess it is the setting that you want, or may be "Reuse Drop Feed tab") ?

Edit:
I have just saw that there is an issue with "Reuse Drop Feed tab", it will be fixed on next version

Than you ;-)

Edit2:
The fix is available here:
https://github.com/dauphine-dev/drop-feeds/releases/tag/0.9.5rc2
Any way, if everything is fine I will push this version Wednesday on AMO

Edit3:
The fix is now available in 0.9.5 on AMO
Why 2 stars removed, there is anything else that I can improve ?