UPDATE 2016-05-06: Now supports the TFS Product Backlog, Board, and Sprint Backlog, with resolved/closed work items green and crossed-out, as well are much improved User Story (Kanban) board.
Do you want your UI controls and whitespace cruft taking up half your browser window, like the default view in the first image? Wouldn’t you like your TFS backlog to instead show as much info as possible, as on the second image below?
You can! Drag this to your bookmark bar (Firefox or Chrome):
TFS Web Compact (for TFS 2015 and Visual Studio Online)
TFS Web Compact (for TFS 2012)
Then, whenever you have TFS web work items or task board open and you want to see more content and less cruft, click it. Be sure to use "full screen view" in TFS and in your browser as desired.
I’ve also made the 2015 version available as a gist.
[Bookmarklets are tiny programs stored inside bookmarks or links. Similar to (but simpler than) add-ons and extensions, they add new tools to your web browser. Bookmarklets are shared on web pages as web links. To add a bookmarklet to your browser, right click on its link and choose the bookmark option, or drag it to your bookmark bar. To use it, simply click on the new bookmark you added.]