During video playback, use the subtitles and the scroll bar to navigate. Clicking the subtitles is a fast way to skip forwards and backwards by small amounts.
If you are on a low-resolution display, the left navigation bar can be hidden by clicking on the set of three left arrows next to it.
If you need bigger or smaller fonts, use your browsers settings to scale them up or down. Under Google Chrome, this is done by pressing ctrl-plus, or ctrl-minus at the same time.