You will not find any other third party Web browsers that support iOS 5.1.1, unless you had previously downloaded some years ago when there was still support for this nearly 10-year old iPad and app developers were still supporting this iPad model.
That iPad is no longer being supported directly by third party app developers any longer.
So, there is NO WAY to watch any online video content on that device any longer.
I own one of these first iPads and many years ago when third party developers were moving away from supporting this early adopter iPad model, I downloaded and installed all of these apps that was able that my newer iPads had including any third party Web browsers and third party email clients, as supoort for this nearly 10-year old device was going away very quickly then.
Time to just simply recycle this device responsibly.
There are very little iOS apps left for that old iPad, if any, that can be initially downloaded from Apple's iOS App Store.
If you do not already have still functioning apps on that iPad, that 2010, 1st gen iPad is really a useless device to you now.
Dontcha think it is high time to look at and purchase either a much newer iPad from a trusted source or look at and purchase a new iPad from Apple or a discounted, refurbished iPad from Apple's Website?
A lot has happened with iPad and iOS in 10 years.
Cameras, Siri, multitasking, Touch ID, faster, more powerful iPads.
That 1st gen, 2010 iPad was woefully underpowered with an underclocked 1.0 Ghz CPU and only a paltry 256 MBs ( NOT GBs ) of internal RAM.
More current iPads have, at least 1-2 GBs of RAM and many of the more current lineup of iPads have 3-4 GBs of internal RAM, now!