In general, no. For Firefox alone, it might help slightly on speed, at least when you start Firefox, but not by much.

For speeding up Vista in general, you could look into what programs are run at startup - here's a link to an article describing how to use the "msconfig" program to disable programs run at start. Be careful about what you disable under the Startup tab, thou - some programs can be quite important (like programs enabling you laptop's hoykeys, touchpad etc). You're welcome to provide a screenshot of the list in the Startup tab, and I can try to make some suggestions. See the Add images and screenshots to Knowledge Base articles article on how to make a screenshot and attach it here, if needed.

Create a new profile as a test to check if your current profile is causing the problems See [[Basic Troubleshooting|#Make_a_new_profile|Basic Troubleshooting:Make a new profile]]

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins"

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files) See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox