To answer a few of your questions :-
UAC is User Access Control, which is Windows default way of stopping you from doing things that could be "dangerous".
Malware protection includes :-
Firewalls which obstruct hackers and arrival of some forms of malware - and just possibly cripple good software downloads.
AntiVirus software that may disable software that it thinks is malware - and sometimes it kills Windows
Behaviour monitoring software that obstructs keyloggers and applications that "phone home" with your bank and credit card information.
The question is, what brand of protection (e.g. Avast, ESET, Norton,) do you have ?
To your problem with delete :-
Under the Firefox Tab every one of the three buttons is disabled until I select an entry.
Only 1 extension has NO in the first column, and when selected this has only the "Disable" button greyed out because NO means it is already disabled
All the other extensions have YES in the first column, and as each is selected only the "Enable" button is greyed out because YES means it is already enabled.
The "Delete" button is enabled as each of the extensions are selected.
When I use the "Delete" button I fully expect that it will not only remove the entry from the startup list,
but it will also Delete it from Firefox and if I should change my mind I will have to download and re-install it - which is a minor inconvenience that costs time but not money.
I only have one PLUGIN which is Shockwave Flash that is almost always a gateway for malware.
The first column is YES and the ONLY button I can use is "Disable", when I click that I am told that CCleaner will close Firefox, so I abort.
I strongly suspect that CCleaner can ONLY implement what Firefox itself can do via Addons,
and Addons can be told to either DISABLE or to REMOVE any Extension
but is only able to DISABLE the Shockwave Flash Plugin - you need to get special software to Remove or Delete Shockwave Flash Plugin(s).
I think you are more vulnerable to malware by having multiple versions of Adobe Flash Plugins,
and I have concerns about obsolete versions of SilverLight Plugins,
but perhaps like .NET Framework the SilverLight versions are built on obsolete foundations.
I will leave it for others to address the issues of obsolete software.
I think that CCleaner is NOT able or willing to Uninstall Shockwave Flash Plugin from the "Startup" menu because this would be inappropriate,
but under the Unistall menu it has the capablity of Run Uninstaller upon many items including Adobe Flash Player 11 Plugin.
I think there is a grave danger that you would need to reinstall Microsoft Office (and possible pay again) if your Startup menu were to Delete Microsoft Office Plugins.
So far as I can see, you are not allowed to use the Startup menu to delete Plugins because this would be very destructive.
CCleaner appears to me be be working perfectly for you in this respect.
I am astonished by your screen-shot, I do not see how your computer can be working
Your screen-shot shows that :-
You are running 64 bit CCleaner,
Shockwave Flash Plugin Files are at C:\Windows\SysWOW64\...
which does NOT exist in 32 bit Windows and confirms that you are using MS Windows 7 Ultimate 64-bit SP1
and yet you only have 1 GB of RAM
Windows 7 System Requirements include "1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)", as per :-
http://windows.micro...em-requirements
I suspect something is horribly wrong with your system.
Just possibly it is only CCleaner itself that is wrong.
I suggest you download from
http://www.piriform....ccleaner/builds
the second item down which is
CCleaner - Portable
Zip file, no installer
4,099 kb - ccsetup401.zip
You can unzip this to a Flash Drive or a new folder in "C:\Program Files",
and it will not disturb your existing installed version of CCleaner.
With the existing installed version closed, just double click on the new CCleaner64.exe,
and see if this also shows that you have 64 bit Windows running with only 1 GB of RAM.
Alan