DavidR
10
Read the comments on the link Simon gave in the first post (not a blog) and they actually mention browsing.
Add-ons provide many useful features and functions, but they can also cause Firefox to become slower. [b]Some add-ons can even slow Firefox to a crawl and make it difficult to use for regular web browsing.[/b]
So by implication some might also have an impact on browsing, though untested.
However, that list does only relate to startup times.
The following add-ons have the most impact on how long it takes Firefox to start up.