Windows 10: Context Menu Pops Up With Every Cursor Move, Without Right Click

Windows 10, Fall Update, 1809 190119-1759, also 1803 & 1806. Dell Optiplex 745 & 760.
This happens in Firefox, Nightly & Thunderrbird when changing tabs and filling forms. Left click anywhere , like selecting an email to open or delete and the menu pops up.
Partifularly irritating in Babas Chess! When I move a piece, the menu pops up.
Sometimes when my opponent moves. It obscures the view of board & pieces.

Tried & failed: replace generic mouse & kbd., mouse settings, safe mode, clean reinstallation, ASC12 & Tweraking.com Windows Repair.

:)

 

Right-click context menu "Run as Administrator" not working

I have the same problem but mine is limited to right clicking the start menu. I can right click everything else and it works correctly, but if I right click the start menu, it doesn't open the context menu and the cursor shifts just a little diagonally to
the top right. I've tried the suggestions above and the new account works fine and the SFC scan came up with nothing wrong.

Edit- also Winkey + X doesn't bring open the context menu either

 

Feature suggestion: Add right-click menu

Suggestion: Please add a Windows 7 Jump-List and/or right-click menu to the GPU-Z icon in the Windows taskbar. Possible menus in it would be "Exit" and "About GPU-Z...".
Maybe also "Switch to tab 1/Switch to tab 2/Switch to videocard 1/Switch to videocard 2" too.
Examples of programs that have such menus are ICQ, Skype, AIM.

NOTE: It seems for a right-click menu, Windows 7 is not needed - it works on WinXP and Vista too.
But even a Windows 7 Jump-list may be good enough.
What do you think?

 

RIGHT-CLICK CONTEXT MENU DELAY

WHEN I RIGHT-CLICK FOR THE CONTEXT MENU IT TAKES 30 SECONDS FOR IT TO POP UP. HOW DO I FIX THIS PROBLEM ???