Roll20 Wiki

Roll20 officially only supports the Firefox & Google Chrome browsers, so it's generally recommended to use them over other browsers, even of others works as well.

Comparison

If you encounter a problem using other browsers, it's recommended to switch to either of these. And no, using any Chromium-based browser like Microsoft Edge is not the same thing as using Chrome. Roll20 often works well on other browsers, but your mileage may vary.

There is no consensus on which browser works best for Roll20, as it seems to vary based on things like what operating system you use(Windows/Mac/Linux), your hardware(physical computer), your ISP, what browser plugins you use, and even what version of the browser you have.

Some have claimed Chrome is faster, others swear by Firefox. It can be a good idea to try out the other (Firefox/Chrome) in case things are more smooth with it.

Plugins

Stylus is a plugin that can change how webpages look, and many roll20 users have created their own tricks and minor adjustments to Roll20 for personal use. Check Show off Your Style 3: Third Time is the Charm^(Forum) for more info and good tricks others have created.

Beyond20 is a popular plugin for people playing D&D 5E who also use DnDbeyond. Among things, it enables you to make dice rolls in roll20 from your DnDBeyound char sheets.

When you encounter problems with Roll20, you should always check if it's caused by some browser plugin you're using, by temporally disabling all plugins and seeing if the problem persists.

Mobile

Roll20 can be used on mobile phones and tables, but generally doesn't work as well as on computers. Some (or many?) users say you can't use the Roll20 video-voice chat on the phone/mobile browser.

A separate Mobile app is under work for Roll20, to act as a companion to using Roll20 on the computer.