If ANY browser gets much slower, it may be because of what you have it set to do. If you have multiple tabs open, or many 'sessions' saved, or a very long 'history' in Mudcat....etc., it can take awhile.
   My Opera loads slower than Firefox, because I have asked it to load with stuff I looked at days or weeks ago. If it gets too slow, I turn most of those tabs into bookmarks and close the tabs.

If a browser merely runs slowly, as in slow to load pages, it is harder to figure out. Perhaps it is sorting out cookies and javascripts, depending on where you are surfing.

But there should be only minor differences between the major browsers in loading time and surfing time.....it is unlikely to be a flaw in the browser.

   The only way to diagnose the situation would be to review your setting and browsing habits.

But...if you want a really, really fast browser, try K-Meleon (