It no longer works, so it falls to one star.
For 3.6, I had no luck bumping Clear Fields by editing the .RDF in the time-honoured way. The .XPI still didn't work.
—So I've uninstalled Clear Fields and now I'm using the combination of Click&Clean and XClear. This combo doesn't do things exactly the same way, but in a few ways I actually prefer it, because, in addition to the field-clearing, it links up your CCleaner for really effortless apres-surf cleans or wipes. You can tweak it to any/all degrees of what you want to clear.