Why browsers are bloated

https://github.com/WebKit/webkit/blob/master/Source/WebCore/platform/Scrollbar.cpp
https://github.com/WebKit/webkit/blob/master/Source/WebCore/platform/win/ScrollbarThemeWin.cpp
Let's reinvent the fucking scrollbar, which every goddamn platform with a UI already has, and make it behave subtly different from the native one!

Right-click a native scrollbar in some other app:
- Scroll Here
- Top
- Bottom
- Page Up
- Page Down
- Scroll Up
- Scroll Down

Right-click a scrollbar in Chrome:
- Back
- Forward
- Reload
- Save As...
...

Right-click a scrollbar in Firefox and Opera:
Absolutely fucking nothing happens!

What the fuck!? How did these terminally retarded idiots get involved in creating one of the most important pieces of software to the average user?

Best associative data structure for element attributes and CSS properties? There's only a few hundred of the standard ones in total, but they'll be retrieved very often, especially the CSS ones.

Hash tables and fixed arrays are the fastest but most memory-bloating, trees are sort of in the middle, and resizeable arrays and linked lists are O(n) (probably n < 10 for elements and < 100 for CSS most of the time) but smallest.

More disturbingly: Why doesn't there seem to be any information on the time complexities of various operations like attribute lookup in existing browsers!?