look at the project requirements, generally look at the project compatibility requirements;

• generally speaking, the compatibility test on the PC side refers to the compatibility of IE. Generally speaking, the compatibility of Chrome and Firefox is rarely tested by people. Basically, if the compatibility test of IE is passed, OK;
• IE compatibility can be divided into two stages. Generally speaking, IE10 and IE8; rarely need to be compatible with IE8 or below (unless it is a government project, some also need to be compatible with IE6), so if the project does not specify compatibility, it is generally compatible with IE10.
• there is no standard procedure for compatibility testing, generally speaking, it is manually tested by testers (I heard that there is cloud testing at present, but I learned that it is basically for APP)
• as for the test platform, you can install browser plug-ins for basic testing, but the compatibility is not as accurate as the real machine test, there will be deviation; more stringent tests should be tested on the real machine or virtual machine.