Do bookmarks slow down a browser?

Do bookmarks slow down a browser in general? Not necessarily talking about start-up alone, but more about the actual browsing of webpages...

Nope, they don't.

What about if you have the bookmarks bar enabled, and many bookmarks in that bookmarks toolbar folder?

Still, no.

It's a circular thing. More bookmarks-> more easily corrupted bookmarks -> bigger file size -> more RAM used -> more Pagefile usage -> slower computer.

If your bookmarks seem to have become corrupted for some reason, you can use the Places Maintenance extension, which has been developed by a member of the Firefox engineering team.

This question was just brought to my attention, sorry for answering on such a old question, but I want to counter the other answers!

They are all correct on all browsers OTHER than IE.

I agree with the other answers - every day browsing is normal.. however, I used to have several thousand bookmarks (now many thousand more!) and, IE does not keep these in a database, it uses individual files.

Whenever I clicked the favourites button, it would freeze the window for some time whilst it generated the list. This is quite annoying and the main reason I switched browsers.