Microsoft have a habbit of making a good OS followed by a bad one.
Win 98 was good.
Win 2000 was bad
XP was good
Vista was bad
Win 7 was good
Win 8 appears to be continuing the trend.
Also, I'm confused by what you mean by "firefox"
Firefox is a browser. Well that's what I thought.
but your phrase
"Thing is , BT Yahoo has installed a password page which now by-passes Firefox and takes me straight to BT emails . Where before Firefox home page appeared , with a box for email , plus news items etc which the Missus likes."
You are not talking about different browsers, but what page loads when you start your browser. And that can be anything.
In my case I don't have my browser set to open any particular page on start up. I have it set to return exactly where it was when I last used it, and I typically have 6 or 7 sites open on different tabs.
I don't personally use on line webmail type email things. Never have liked them. So to me emails is completely different to web browsing. I just open up my email program and press "send and receive" and there are my emails. It remembers all user names and passwords. Of course it's not "portable" like webmail, I can't just use any old puter. When we went down under, I had to set up all my email accounts on Mrs PD's laptop so I could use that while away.
So what browser are you actually using? Do you have more than one installed?
I hate BT and Yahoo, who seem to have joined forces. That caused me no end of trouble when I switched my broadband to BT recently and I was forced to choose a @btinternet email address (that I don't use) and that hijacked my Yahoo email. I don't use Yahoo for email, but do use a Yahoo group for the local Freecycle, and somehow this new BT email took over my yahoo account. The only solution was never ever use the @bt internet email (which I don't want to do anyway)