Thanks for providing these instructions. My usual way to get to some setting in Firefox is to use the search box but it seems that Mozilla is actively hiding this one by excluding it from search, ie if you type "advertising" into the settings search box then there are no results.
That is because "Allow web sites to perform privacy-preserving ad measurement" doesn't have the word "advertising" in it. Granted the current phrasing a bit awkward and may have a certain degree of deliberateness behind it.
It seems the search matches on the text of the option, not the section text. The text of the option is "Allow websites to perform privacy-preserving ad measurement" and the search for me brings up the option (and of course anything else that matches) when I search for any of that.
