Slow browsing could be rooted on lots of possible causes.
Default RouterOS IP settings are perfectly fine, you are not going to magically fix anything by blindly changing them.
Disable TCP Syncookies, accept redirects, and accept source route, (i.e. restore to its defaults) and see if it makes a difference.
If slow browsing persists, usual suspects are slow DNS, (due to slow DNS server, or Internet line related problems) or plain wrong configuration.
If that's the case (plug a computer directly to the internet line and see if problems go away), I'd suggest resetting to defaults and starting over.
Yes Guru you are right, i did what you suggested , Unchecked/Disabled
TCP Syncookies, accept redirects, and accept source route and now it is okay all over ,
Thank you so Much Pukka Guru