Another thing that speeds up the booting time of Firefox 3.5 is clearing the temporary folders for every browser on the system. The new version uses these temporary files to generate random numbers, so if you have many files, it will take a long time to startup.
Though firefox does not take too long to open on good processors now a days,it is really slow on a bit slow processors,you can reduce the history size of firefox as it keeps history of 90 days by default,and at startup they are loaded.
For speeding up surfing you can use Tuneup Utilities or Advance System Care for optimizing the browser.
firefox stores 4000 history entries by default. Reduce it to 1500.that ought to be enough for one session.
NoScript disables scripts for you, adblock blocks ads. but firefox 3.5 takes ages to start up.
Mozilla links wrote a blog post about this, it basically involves cleaning out these folders once in a while:
C:\Documents and Settings\*user*\Local Settings\History
C:\Documents and Settings\*user*\Local Settings\Temporary Internet Files
C:\Documents and Settings\*user*\My Recent Documents
C:\Documents and Settings\*user*\Temp\
you could probably set up a batch file to do that for you.