I switched from this to SSS because there was always a delay from when you right click selected text to when the context menu option to search appears. Works as advertised otherwise, but I would love an update that fixed this. Seeing as it hasn't been updated since 2019, I somehow don't see that happening.

Edit: Found an extension as simple as this, but without the delay: https://addons.mozilla.org/en-US/firefox/addon/simple-context-search/