As suggested, i´ve removed avast 8 and install 9. Now, webrep is installed on Opera 12, but doesn´t appear in bar or in google search. Something that i can do?

Avast online security (ex WebRep) is not supported in Opera 12.xx (Presto) anymore.Also it is not supported
in Opera Blink.Use WOT with Ghostery or ABP with EasyPrivacy list.

So, if it´s not supported, why the extension is installed ?

Maybe it is leftover from previous Avast version ?

Why isn’t Opera 15+ supported? Same engine as Chrome, it shouldn’t be too hard.

Not the case! First, i have done a clean install. Second, if i open the manage extensions, the version i see is the new one, not the previous.