It's a common story -- people use browser A, start noticing a variety of problems, switch to browser B and everything is so much better. After a while, they start noticing a variety of problems, switch to browser A, and once again everything is so much better.
Those people are not being stupid, that is their real experience.
Sometimes the problem is in a web site (an update starts leaking memory, for example) and whatever browser is running gets blamed.
Sometimes it's just natural human bias—we want to see patterns, and we want there to be a solution ("just switch browsers!"), so we get selective in what we notice and don't notice.
Sometimes it's because profile cruft piles up, and resetting would fix it.
Sometimes the problems really are in one browser and not the other. There are plenty of legitimate problems to be found, and things change pretty rapidly.
How would resetting the profile help? It means losing addons and their configuration, the bookmarks, the open sessions and the tabs, the history, the about:config settings.
It means losing a lot of stuff, yes. It sometimes helps because some things slow down as state is accumulated. So resetting can speed things up, at the cost of losing all of your state.
But the comparison point is switching browsers, which also loses lots of state.
(In both cases, you can import a subset of your state into your new profile, and you'd probably get most of the performance advantages.)
I believe all browsers have been improving in their resistance to the accumulated state problem, but I also believe that all browsers are still susceptible to it.
For what it's worth I haven't had an issue with Firefox for at least five years. And in the entire history of using Firefox I've never had a problem that was solved by a profile reset—though that might be because I'm a technically savvy user who can troubleshoot with relative ease.
Any time I've tried switching away it's more to see if I'm missing out on something... and it turns out I'm not.
You're both right.
It's a common story -- people use browser A, start noticing a variety of problems, switch to browser B and everything is so much better. After a while, they start noticing a variety of problems, switch to browser A, and once again everything is so much better.
Those people are not being stupid, that is their real experience.
Sometimes the problem is in a web site (an update starts leaking memory, for example) and whatever browser is running gets blamed.
Sometimes it's just natural human bias—we want to see patterns, and we want there to be a solution ("just switch browsers!"), so we get selective in what we notice and don't notice.
Sometimes it's because profile cruft piles up, and resetting would fix it.
Sometimes the problems really are in one browser and not the other. There are plenty of legitimate problems to be found, and things change pretty rapidly.