I was notified of the existence of the new version but delayed downloading it, on the principle that "completely new" software often has many bugs. However, the automatic update system moved me to the new version, since when, instead of being "twice as fast" everything takes much more than twice as long. I have been estimating response times by counting "1 and 2 and..." and find it can take anything between 5 and about 20 seconds to respond to a click, even for just opening or closing a tab. Typing anything in the new version is a real pain as I can get a couple of words ahead of the screen in spite of being a slow typist and then have to stop as I am not sure it is actually working. I had trouble logging in to my emails, I suspect because Firefox was sending my password a few characters at a time, in spite of my checking there were the right number of characters shown on the screen before sending it. Also one of the tiles on the New Tab tab refuses to be deleted! In case there had been some problem with the update I uninstalled and then reinstalled Firefox but it has made no difference.

Is it possible to return to the old version and, if so, how? If not then I shall just have to abandon Firefox ( I should point out that even Microsoft gave the option of choosing when to move to Windows 10 and going back if you didn't like it but Mozilla has been totally arrogant in introducing this new version).