Site-specific hack to make expanded tweets scrollable.
Site-specific hack to make expanded tweets scrollable.

Twitter is an important site and Vimium's scrolling is currently broken
when a tweet is expanded.

In my opinion, the existing bahviour is so bad and that a site-specific
hack is warranted.

Fixes #3045.

decaffeinate-examples/vimium,smblott-github/vimium,poacher2k/vimium,philc/vimium,philc/vimium,gdh1995/vimium,gdh1995/vimium,poacher2k/vimium,smblott-github/vimium,gdh1995/vimium,poacher2k/vimium,decaffeinate-examples/vimium,smblott-github/vimium,decaffeinate-examples/vimium,philc/vimium