Re: Why is "Remember Passwords" option grayed out?
Sounds that some prefs are locked.
Do you see any locked prefs on the about:config page if you click the Status header to sort by status?
To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.
Start Firefox in Troubleshoot Firefox issues using Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).
Don't make any changes on the Safe mode start window.