Once you interact with the player on Youtube, it can be difficult to redirect keyboard output to the web page. On many sites, simply clicking on the page outside the player will do it, but in the past Youtube's player has proven more tenacious.

As of about a year ago, users had discovered these workarounds:

(1) Full screen the video and then switch back

press f then Esc - focus will move back to the page

(2) Switch to another application window and then back

press Alt+tab then Alt+tab - focus will move back to the page

(3) Click on a different tab then click back - focus will move back to the page

But obviously none of these is convenient...

Regarding switching what Home and Page Up and Page Down do, I'm not sure I understand what you mean. Could you describe that in more detail?

You may have switched on caret browsing.

• http://kb.mozillazine.org/accessibility.browsewithcaret

You can toggle caret browsing on/off by pressing F7 (Mac: fn + F7).

• Tools > Options > Advanced > General > Accessibility: [ ] "Always use the cursor keys to navigate within pages"

Note that this is an accessibility feature of Firefox.

• http://kb.mozillazine.org/Scrolling_with_arrow_keys_no_longer_works
• http://kb.mozillazine.org/Accessibility_features_of_Firefox