Had to create an account just so I could recommend and review this extension, which works great, with a perfectly minimal footprint.
I'm a coder, so I spend much of time online, and many sites like to steal focus when I try to search the page for a term using the slash key; which means that I then have to instead click on the Firefox File Menu Bar, then click Edit, then click Find in This Page.
This extension perfectly stops websites from doing that.