Firefox cannot find some websites

I've been wanting to comment that I've been having the same problem Westside mentioned from time to time (just since having installed FF1.5) - but the last thread under this title scared me off from posting anything (thanks for closing that one, Ramona!).
Now that I am free to start a new thread without being (justifiably!!) chastised for duplicating a previous post, I just thought I'd make mention of my own experience to add to the wealth of data here.
The "Firefox can't find" message is sporadic in my case - a webpage may work fine for me one day, but I get the "can't find" error the next day. I do use tabs, but sometimes I only have a single tab open when the message pops up - I haven't noticed any correlation between the error messages and the number of tabs. And I can't think of any instances where I've gotten the message using Bookmarks, though I haven't been using too many of those lately.
As in Westside's case, clicking on "try again" doesn't cut it, but clicking "reload" works every time - so like him, I don't consider it a major problem (especially since it only happens once every few days).
I just cleared out my cookies this morning, and I'll see if that has any noticeable effect. I only have one profile (though my roommate has his own too, so I guess that really makes two); Firefox 1.5 is our main brower (I only use IE for Windows updates and if I have a problem with a particular site using FF). As far as potential complexities, I admit to having become an extension addict - I have 14 of them right now, BUT, just for the record, the "Firefox can't find" messages predate my extension frenzy.
I'm not necessarily looking for help troubleshooting here, just posting an observation (although I'm always open to suggestions, if anyone DOES want to throw some in!).

 

Rebecca,

I promise not to make you walk the plank if you duplicate a post!

When this occurs, is the "page not found" for an ad, i.e., doubleclick, or something similar? I have had that happen occasionally also, and DadDad sent me a link to this page, which may interest you:
http://www.pcworld.com/news/article/0,aid,123910,00.asp

This is old, goes back to May, but reportedly is fixed.

 

Rebecca,
I have not had the page not found error, since I last mentioned it. Right now I am having a page load error, which is found in all browsers from the Omaha World-Herald website . It was ok earlier today, and it is a real shutdown. It happens at times.

 

Ramona,
The only two instances of the "FF can't find" message I can specifically remember were when I was trying to access hotmail.com and therainforestsite.com, i.e., I wasn't clicking on ads - I'd actually typed in the urls. Probably too soon to say if clearing cookies has made a difference, since the "problem" occurs pretty infrequently to begin with, but I'll keep an eye out.
No problem with Westside's Omaha World-Herald website.

 

Rebecca,
I did not have any problem with any website two days in a row.
My feeling is that those are temporary shutdowns or glitches.
In a related fashion, I don't know if you ever tried the CBC online , but I have had some unusual problems with Radio Two, in the past two weeks, and it does not matter which browser I use. For a period of time, the embedded WMP would buffer, and start counting up, but could hear no sound . I sent a feeback, and the next day it worked. Then on Saturday morning, I could not connect at all.
This happened only with the Radio Two connection. Radio One has always been good. I have not tried since Saturday. Just wondering, but this seems to be at the cbc.ca end.