webpages not opening in opera

Works on Firefox?, Works the "HTML only" option on Gmail?, Opera installed from Repos?

I downloaded the browser from : http://www.opera.com/download/
All the webpages open on Firefox.

So why you dont use Firefox? You think is better Opera? Why? I use it in 2004-5 with ADs in Windows but I think Firefox 3 is more custoimizable with addons but popups some times opens...;) . I use new Konqueror that FINALLY can load videos from youtube (initail KDE 4 versions didnt) but didnt save images (in prev KDE 3 versions did!). Firefox 3 cosnume huge RAM and more as time passes, Opera too?

The thing is that sometimes two browsers become necessary. I have got more than two gmail accounts, and need to sign in into both at the same time, and at that moment, when a second window is opened I am already signed in into gmail as one user, and my inbox shows up. So, I cannot logout for signing in as another user as doing this would log me out from the previous window as well. The same is for any other account, in case a second window is opened in the same browser. I am already using Mozilla Firefox and it is working fine. But due to the problem mentioned above, I need another browser.

As suggested, you can try Konqueror ("Applications" menu, "Add/remove"), it is working pretty well and has a engine that is similar to the one in Apple Safari or Google Chrome.
Anyway, it should work with Opera... Can you try again to re-install it? First remove it by using the application in the menu "Applications" -> "Add/remove". Then follow those instructions:
http://ubuntuexperiment.wordpress.com/2008/11/09/installing-the-opera-web-browser-on-ubuntu-810/

I have been myself following those instructions, and I can use Gmail with Opera 9.63 on Ubuntu 8.10.
If you still have the problem after that, could you show us a screenshot of how it looks when you try to open Gmail in Opera?

I coretc: Konqueror saves images but I dont know how to save a web+images so everytime I need to save a web with images (wikipedia article) a have toopen with Firefox 3, annotying..Idont know why have removed so useful and important option. At beggining I use Firefox 3 for taht and to view videos as Konqueror dont showed well, even when flash plugin installed. I like Konqueror cause is faster and lighter than Firefox 3 for example for posting quickly when crahses occur the Bug Manager uses it to report it to KDE bugs or here in Launchpad. For a wide and more varied navigation experience I use Firefox: videos, access webs with a los of Java..

I don know that Opera was for Linux! and i dont understand why you have more than 2 mail accounts, iv one and Im really busy for that! and why to sign both same tome? If its only to sign in a forum/blog you can use Konqueror not?

I leave Opera as I founded a bit bloated (in Windows) nd some webs werent displayed welll, in 2004-5. But some pople says that is the best Navigator, opinions, It's a matter of taste...why you like it?