Today I also joined to people who lost over 100 tabs. How this was not an issue and now is? Why closed tabs are not in history?!
I've been using Opera since 2006, but I fell this is too much for me. Moving to different browser was a problem, but now I don't have to move 100+ tabs to new browser.

Opera 12.16 is quite old, and developers do not support it. Probably (I haven't tested it) there are some JavaScript errors on outlook.com. With time more and more pages will not work