If you want to make a customizable browser, give us the option to not install such unnecessary addons. The browser already seems to use as much memory as chrome, it does not need to waste any more.
I used Opera pre-12, and the reason I did so was because all of the features that I wanted were baked-in to the browser, which meant that they went through the same quality controls and integration testing as the rest of the browser. There was no separate step of updating add-ons, or even worse having outdated add-ons with no compatible version. Everything Just Worked.
Granted, some of the features were not as feature-complete as comparable Firefox add-ons. E.g., tab-stacking is strictly inferior to tree-style tabs because there is only one level of collapse. But everything I wanted was already included, at an acceptable-enough level that for me, it outweighed the cost of having to comparison-shop for mouse gestures or custom CSS solutions or whatever.
FWIW, Opera never felt "bloated" to me. It had crop-tons of features, but for whatever reason that didn't translate to a feeling of bloat. The browser was fast and responsive, and the pile of features never really got in my way. Every once in a while, I would read about an interesting Firefox add-on, dig into the Options menu, and find out Opera had the feature all along, whereupon I would drag it onto the UI.
Personally I like having the email built-in to the browser because it means I don't have to context-switch to see the status of my inbox. But that's a personal quirk.