I would not recommend installing a newer version of OS X than 10.8.5 Mountain Lion, which isn't much better off with browser support. The reason being it will be slower, due to lack of graphic acceleration in OS X 10.9+, which my Late 2006 iMac also suffers from.
I would recommend installing Linux alongside OS X. This will allow the MacBook to run a current, supported version of Firefox or Google Chrome which also performs better on sites like Netflix and YouTube. Linux Mint has made my Late 2006 iMac more useful, and able to run most of the current Linux-compatible software.