I recently added some plug ins. I have 3 versions of GIMP on 2 PC's. This is GIMP 2.8. When ever I right click, I get the same menu found at the top of GIMP, in drop down format. Today I find it conflicts with the function of closing the selection using the free select tool. When attempting to close the selection using right click, you get the drop down menu instead. Any one know how to remove this. I also use london smoke blue theme, and may have hit something in preferences. Thank you.

AFAIK not possible without recompiling the Gimp code. Maybe you are thinking of some other application. Right-click to complete has never been the way to finish off a free selection. The info panel bottom of the Gimp 2.8 window gives the options Return commits, Escape cancels, Backspace removes last segment

The right click on the window brings up the menu structure which leads to the option to use 'tear-off' menus.

30 second example: https://i.imgur.com/woJrR73.mp4

This a normal behaviour (same behaviour as 2.10) https://docs.gimp.org/2.8/en/menus.html#context-menus
Citing the above link: "[right] Clicking on an image window displays the Image menu. This is useful when you are working in full-screen mode, without a menubar. "

To close a selection you left click or double click, not right click...

Thank you friends, I got it figured out. Always great help here. This is a good forum.