Bug 804935 - TypeError: window.tabs is undefined

It was a regression during fennec implementation of windows and tabs. A `ChromeWindow` was used instead of the expected `BrowserWindow`.
adding a test for disposables that unloading one loader does not affect the other
create new branch for low-level api cleanup
work on content pages
work on content pages
more work on 'content'
work on deprecated
working on deprecated
more on deprecated and events
add event api ref
fix code sample
Merge branch 'master' into llapi-cleanup
...
more updates to low-level API docs
window/utils
created tabs/utils.md
tabs/utils
finished draftnig tabs/utils
fixed toc names
Merge branch 'master' into llapi-cleanup