I solved my problems by using the latest dev-build of tab-mix-plus (0.3.8.3pre.100319) as described at http://www.webupd8.org/2009/07/install-tabmix-plus-in-firefox-35.html
my firefox version is: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100214 Ubuntu/9.10 (karmic) Firefox/3.5.8 GTB7.0
I solved my problems by using the latest dev-build of tab-mix-plus (0.3.8.3pre.100319) as described at http:// www.webupd8. org/2009/ 07/install- tabmix- plus-in- firefox- 35.html
my firefox version is: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100214 Ubuntu/9.10 (karmic) Firefox/3.5.8 GTB7.0