How do I search a page using a regular expression in Firefox?

Since the other alternatives offered here have been left in the dust of technological change, and rendered incompatible with latest versions, I'll drop the two current compatible addons I found (though I haven't tested them): Regex SearchSearch in HTML or Highlight using Regular Expression (REGEX) and output the results using template, with saving profiles functionality, you need to know 'basic' Regular expression to benefit from this plugin {find+}{find+} is a simple Find-in-Page extension hos…