performance diff extensions vs plugins?
Is there a measurable performance difference between equivalent chrome extensions and opera plugins?
That word usually refers to binary SO files (shared object) or dll files (dynamically linked library) that use the NPAPI to communicate with browsers for the use of embedding their functionality in a web page. The Adobe Flash player is one such plug-in. Plug-ins in this case are not used to extend the functionality of the browser.
The things at addons.opera.com that extend the functionality of Opera are called extensions just like they are in Chrome. Chrome extensions can be install in Opera via the Download Chrome Extension extension.
So, using the word 'plug-in' when you mean 'extension' can confuse us sometimes.
As for your question, if you make an extension for both Opera and Chrome and make it the same way, they should both perform the same in Opera. Now, there might be a Chrome extension and an Opera extension that does the same thing where the implementation is different. In that case, one might perform better than the other in Opera. Just depends. You have to inspect both the Chrome and Opera versions of extension 'foo' to see if everything code-wise is the same.
In short though, I don't think you need to worry. I guess it's possible that the Opera version of an extension is slower if it uses some extension APIs that Opera supports and Chrome doesn't.
Yes, they differ!
Plugins are fast because they are compiled as binary program modules.