tb.ask.com seems to have taken over but Firefox seems to be in background
The Firefox symbol has gone from the top left hand side of the home page. Next to the "File, View, etc" toolbar is a box with a red cross which gives message "login failed -check username and password". The Telstra homepage is still displayed and internet and gmail works but on checking Control Panel for internet options it lists "ask.com". This situation seems to have occurred sometime last week.
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hello, this sounds like a problem possibly caused by adware on your pc.
please go to the firefox menu 
> addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc).
also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there.
finally, run a full scan of your system with different security tools like the free version of malwarebytes & adwcleaner.
Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware