Flash with Firefox/Opera without Installation

Since last week I've been wondering if there was a method to install Flash on only Opera without affecting Firefox. While Flash can be annoying and possibly compromise your security, you cannot deny it becoming a standard these days for so-called "interactive dynamic websites". Let's see if Microsoft's SilverLight can do any good to rival Flash.
Well, I've managed to find a workaround (credits to Fabio Varesano) without having to install. Might be useful for some of you or maybe not. In any case, this could well be informative. People behind administrative constraints might find this useful assuming they have access to the local drive where the installation of Windows is located.
Here's the workaround:

1. Download XPI archive of the Flash Player Plugin to your hard disk. fyi, XPI archives are like ZIP files.
   
2. Extract the files in the archive using WinRar or your preferred file compression app.
   
3. Copy the files flashplayer.xpt and NPSWF32.dll to %APPDATA%\Opera\Program\Plugins\
   %APPDATA% is the folder which holds your applications profiles and settings. (You can open this folder simply choosing "Start → Run → Type in %APPDATA% → OK")
   
4. Restart Opera

If you want to install it on Firefox instead, here's the steps:

1. Download the XPI archive of the Flash Player Plugin to your hard disk.
   
2. Extract the files in the archive
3. Copy the files flashplayer.xpt and NPSWF32.dll to %APPDATA%\Mozilla\Plugins\ where
4. Restart Firefox

Note that these steps are obviously only for MS Windows.
Rationale behind this? Nothing really. This is just a matter of preference. Some of you might say, why go through all the trouble when there are good utilities/add-ons around the net like Adblock, Flashblock etc. Well, I want to keep Firefox flash-free; I refuse to go through installation.
Then again ,why not just use Microshit's Internet Explorer (IE) you might say... Forget IE unless you're still using version 6. What about version 7? Apparently, there are problems running this bugware browser with the latest Flash 9 esp. on crappy Vista. Like most of the "victims" around this netsphere, I still haven't found a solution. My major prob is that IE7 crashes/closes/gets raped suddenly when I open certain sites or certain pages (hell, I can't even create a new post at Blogger.com using IE7, even if there's no Flash content). Adobe's re-installation solution doesn't work. Bah.
I've a feeling them bloody buggers don't even know what's wrong or worse, what they are actually doing. I hope this is not intentional from Microshit. With the introduction of Silverlight some time ago, I don't see any reason why they won't do that. Marketing strategy eh? Someone enlighten me please.