I can't say I notice any additional start-up delay. It was already rather slow for me as I've got too many tabs open!
However, Since FF 3.6.6 I seem unable to print anything?! If I try to print or print preview, I get a massive delay when the browser is unresponsive (several minutes) and finally an empty dialog box, "Warning: Unresponsive script". The print preview then appears, but actually printing gives a "Printer Error - An unknown error occurred while printing".
When trying to print (without preview) I do at least get a message in my "Warning: Unresponsive script" dialog... "Script: chrome:://firebug/content/chrome.js:1242". A compatibility issue with Firebug!? But disabling Firebug does not sort the issue? I just get a different unresponsive script... "Script: chrome://global/content/printPreviewProgress.js:23"
Anyone else have this issue?