hello Asgardindustries...

Many site issues can be caused by corrupt cookies or cache.

   Clear the Cache and 

   Remove Cookies
   Warning ! ! This will log you out of sites you're logged in to. 

Type about:preferences<Enter> in the address bar.

   Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
   Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now. 

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

Hi Rob, what kind of error message or other odd behavior do you experience? Did the provider say they were working on a solution?

Thanks for your help Ankil. Had already tried clearing cache and cookies. Going to try the safe mode suggestions in a minute.

Thanks for your help jscher. No other odd behaviour and provider (while very polite) didn't seem to think it was their problem, as they hadn't changed anything and no other browsers were generating the problem. The only error message I'm getting is the one you get if you enter an incorrect username or password - which I'm not.

I just can't log in to my email - as if I was mistyping the password, though I'm not.

You get the identical response whether you type your correct password or an incorrect password? No subtle differences?

Thanks for your help, both of you. Resolved by changing both email account provider and email passwords, and reinstalling Firefox.

Cheers Rob.