Your question is a bit confusing, and it seems that you don't quite understand who and what can view your internet activity:

• Private browsing mode simply leaves no record of the sites you visit in your browser. There are so many other parts of the chain that can keep records. Example: Your computer could have tracking software (installed intentionally or maliciously), many routers have web logging, your Internet Service Provider can view the sites you visit, your employer if you are at work, the government has extensive tracking programs as well. Private browsing won't defeat these tracking techniques. It basically only prevents people who have physical access to your computer from looking in your history and seeing the sites you visited in PB mode.
• Your employer can't just request to see the sites you visit when you are at home. The only reason your employer could see the sites you visit is it you take your computer to work and use your work network to access the internet (and the employer has enabled logging on their network hardware) or you have a work laptop and take it home and it has logging software installed on it. Many employers have policies against using work equipment for personal. But there is no way that your employer can call your home ISP and ask to view your internet history.
• Your ISP keeps a record of the sites you access, but won't release that without a court order (or to the NSA....) so unless you have a court order or a snoopy ISP employee who has an axe to grind and is viewing your internet logs illegally you don't really have to worry about that.
• It's possible you have malware on your computer that is tracking your internet history. Troubleshoot Firefox issues caused by malware

Sorry you are having problems.

I think you may be misunderstanding the situation in which an employer will be able to monitor your activity.

For an in depth discussion of this subject you will need to find some forum specialising in discussing security. One thing you should do however is check the current PC for any form of malware. Another is to to follow good standard practice regarding security and privacy.

Your ISP obviously is able to monitor your use of their service. In a similar way an employer may be able to, especially if they provide the computer and the computer network.

Mozilla Firefox does not really get much data from you. Your bookmarks are normally just on your own machine. If you use the Firefox sync service then the bookmarks get copied to a Mozilla server but they are secure and encrypted.

I am not sure what you mean by

One of their members I worked closely with was stalking my email and browsing history without my knowledge. 

Was the person part of your Company IT department ? or did the person have access to your machine and its passwords? If your suspicions are correct possibly those activities would be criminal acts in some jurisdictions, but that is not a subject to discuss here.

Obviously if you think someone knows your email passwords change them, and after ensuring malware is removed change them again.

I will add some useful links, and follow on with the standard advice about malware.

• https://www.mozilla.org/en-US/firefox/desktop/trust/
• Create secure passwords to keep your identity safe
• Use a Primary Password to protect stored logins and passwords
• How does built-in Phishing and Malware Protection work?
• General listing https://support.mozilla.org/products/firefox/privacy-and-security
• Windows MIcrosoft http://www.microsoft.com/security/default.aspx

You should ensure you use a password when logging into your computer, and that your router is secure, but again those are subjects outside the scope of this forum

Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Did this fix your problems? Please report back to us!

You can also check the connection settings to see if you are using a proxy.