... so you think its my os ?
Unfortuately many new websites require new(er) browser versions, and Firefox will no longer update theirs for Tiger.
Apple released the final Safari update for Tiger two years ago.
Your PowerBook can be upgraded to run Mac OS X 10.5.8 but I do not recommend it. First, Tiger is probably the best OS for your PowerBook G4. Second, retail versions of Leopard are unreasonably expensive.
I understand this must be frustrating, your PowerBook G4 is a fine computer, but as it is about a decade old it precedes YouTube, Facebook, the iPhone, and many other things no one ever thought it might need to do. The world moves on, but hardware remains the same.
Macs last a long time but every one eventually reaches the point of functional obsolescence.
You will want a new one under the tree this year
Yes, if you are using websites that require Java, make sure that you have updated Java in Software Update. Run Software Update and install everything that it recommends.
However, you will run into the same problem with Java. Some newer websites simply will not work with older Java versions, and newer Java versions will require newer versions of Mac OS X.
See what I mean?
Leopard gets a bad rap for some reason. I have four PowerBook G4s here at home (two are my personal Macs) and Leopard runs just fine. Max your ram and you should be fine Compared to Tiger it's modern and it works.
I wouldn't go back to Tiger if you paid me. Almost any PowerPC app that's left will only run on Leopard and Tiger for me was unstable, particularly in a network environment.
Moving along, you can't expect a version of Firefox that is 15 versions out of date to function the same as the latest. Updating Java is all good and that, but Michael Wasley's suggestion is better. There are alternatives. Most of the users on these forums seem to be unaware that there are still many versions of browser out there that are PowerPC. It's not necessary to buy a new Intel Mac just to get a new OS that will run Intel Firefox.
In addition to TenFourFox (v10 stable, v17 soon to be the stable version) there is Aurorafox, which is based on T4Fx code and based on Mozilla Firefox nightly builds.
There is also a hack to the Flash plugin that fools websites into thinking your PowerPC Mac is running the lastest version of Flash. You can also view Youtube in Mactubes which is a PowerPC app just for viewing Youtube.
In short, the PowerPC platform is not dead yet.