Problems with FireFox... anyone else?

It started on my main computer about 6-8 weeks ago, sluggish and crashing. I got tired of it and moved over to Opera. I'd bounce back and forth, and lately it's been "OK".

Today, I had been working on my laptop a lot, then this evening upon opening the FF browser, it had that pop up window saying something about "checking for add-ons" so I assumed it did an update.

all of a sudden, I could not connect to the internet, but only with FF. IE was just fine. I disabled add-ons, nothing. Rebooted, nothing. after each -- I'd check IE, which was fine. So I did a System restore. When that was completed, now IE would not connect either. When i ran troubleshooting, it said something about a part of "Nortons" was not installed properly. ~~ What the heck??

So, now i went in and disabled the Anti-virus and now everything works.

What gives??

I attempted to install Opera on my laptop [5 yrs old, Win7] and it would not install. The window just said.... Downloading....... and the percentage thingy never moved.

any idea what may have happened??

thanks in advance for any assistance,

Terese