18.0.2 won't install.

Update won't install. If I check for updates manually, it searches and searches and searches some more, and eventually I have to close it down. If I wait for the popup asking me to download and install, then this proceeds automatically and presents a large popup with a Finish button; if I press this nothing happens and eventually I have to close the window manually. 18.0.2 has not downloaded or installed. Very tedious! [PS I note that the troubleshooter installer is also hanging now. Everything else installs OK on my laptop, but not apparently Firefox stuff...]