If the internet is slow in all the browsers, it worth to investigate other issues as well, please try these:
(A) Check the internet connection speed with the ISP, run a speed test.
(B) Update the Java, flash, .NET or any other dependencies.
(C) Minimize on addons, extensions etc.
(D) Update the antispyware software and run a scan.
(E) Optimize the browser settings.
(F) Check for antivirus software monitoring the browser.
Here’s to Good Karma