To be fair, having checked, several of those addons do (now) say they're for older versions.

You could always try some others; e.g. for New Tab Button on Tab Bar try New Tab Button on Tab Right (adds an IE style button on the tab bar - works fine), for UnPlug use the aforementioned Video Download Helper (and add the automatic conversion tool).

As for some of the others, I've got the AVG search and surf shield addon (I use AVG internet security - AVG 8), I gave up with Google Toolbar long ago and I wouldn't even bother with the likes of Adblock, ForecastFox, or GetMail. PicLens, however, I might give a try - someone else recently mentioned this one to me.