My preferred browser is Opera and it is the one I have always used when testing my speed.
I upgraded Opera about ten days ago. Since then every single test on Speedtest with Opera has been at 10-15% of what I should be getting and the ping time is long.
Still I didn't feel that my speed was slower then usual.
I tried the test with Firefox and IE and both showed my usual normal speed.
I've done this comparison a dozen times since always with the same result.
Has anyone ever heard or read of an erroneous report due just to the browser one is using for the test?
By the way, even with Opera it's only an issue at Speedtest, Speakeasy tests OK.
I know that in the mobile version of Opera, at least by default, it routes everything through their proxy server, which is supposed to improve speed on low-bandwidth connections. Could that be what's happening for you as well?