It is working for me, but not quite like it used to. Here is what I do....
After I click on "RootsSearch for xxxx"....On the first page I put my email address and WikiTree password (not my WikiTree ID.) On the second page, I put the WikiTree ID of the profile I am searching (not my own WikiTree ID.) Then I am given the option of which site I want to access, among them are FamilySearch. I click that button and I am taken to FamilySearch's results.
I don't know if it makes a difference, but I use the Chrome browser on my laptop