1. Does MS or Adobe automatically uninstall/download updates?
2. Am I required to uninstall the old adobe acrobat reader dc before installing the update?
3. Am I required to download Adobe Reader in firefox & internet explorer browsers?
Acrobat Reader is an Adobe product. It should update automatically from Adobe. MS has nothing to do with it.
You shouldn't need to uninstall the old Acrobat Reader.
It doesn't matter which browser you use to download Acrobat Reader. There may be a plug in associated with Reader for the specific browser you use to download it with. You may be asked if you want to install the plug in. The plug in will allow which ever browser you used to download Reader to read pdf files right in the browser. So download Reader using the browser you use most often.
If you're going to download a fresh copy of Reader instead of updating your current versions (by using the Update button), I suggest you uninstall your currently installed version.
I uninstalled Adobe Reader using revo uninstaller pro. I then installed a fresh copy of Adobe Reader using my firefoz browser. Is there any advantage in using the "Firefox Foxit Reader" for firefox & the Adobe Reader for Internet Explorer?
Foxit Reader is not part of Firefox. It's a different company. Foxit Reader and Adobe Reader both read pdf files. I used to use Foxit Reader. Don't remember having an issue with it. Use whichever you prefer.