So, are you having problems or just getting the warnings?

I've been using Unbuntu with what appears to be Firefox and have not
had a problem on any site.

What I do have a problem with is IE 7.0. If I open and close 7 or 8
tabs, the thing crashes under XP. Firefox does not have this problem.
Now that I am looking to go to Linux, I have even less desire to run
IE. Personally, I prefer the Firefox interface.

Let us know how Opera works out for you.