>>>>>Thanks, Sergey. I'd rather avoid 3rd party extensions but I might look into it later.
>>>>
>>>>It seems that several things that are built-in in Opera, must be installed separately in FireFox.
>>>
>>>For me several things are not working. I think, it's because of firewall, but I were unable to activate them and have to live with limitations :(
>>
>>What version of Opera are you using? And what is not working?
>
>Version 7.54 Note, when I click Help, About, it opens a window inside the current window, e.g. UT. So I had to re-login to UT.

Strange. It opens in a separate window for me. (7.51) Perhaps some option. Anyway, once you are aware of this, you can open another window first.

>When I use search, I can not search by specific user (e.g. when I click on this button, the new window is not open). I have similar problem with other popup windows...

Strange, that seems to work for me, too. Perhaps you disabled popup windows?

I have it set to "block unwanted popups", which I think is the default, rather than "block all popups".