Implement in FF Extension: Highlights and scroll to annotate

**Problem:**
The firefox bookmarklet doesn't allow for the same complete suite of usability features the chrome bookmarklet or extension offer.

Users cannot highlight or scroll to annotate with the Firefox bookmarklet.

**Question:**
Are these actual bugs, or features we never created for the FF bookmarklet?

**Possible Remedies**
- Implement FF extension? https://trello.com/c/VFLEZOaq/139-epic-firefox-extension
- Update PDFjs? https://trello.com/c/tpeSKNZu/80-update-pdf-js-and-document-the-process-of-doing-so

Labeling this as a P5, b/c this needs to be characterized further to know the scope of work needed to fix (if a bug) or build features (if it isn't a bug).

Start by reviewing the Firefox bookmarklet limitations described here and the linked Trello cards for the Firefox extension and PDF.js update. Compare the available Chrome features with Firefox behavior, then establish whether highlighting and scroll-to-annotate are missing features or bugs. Done means the scope and implementation path are clearly characterized.

Written by the indexing model from the issue text.