Security flaws browser vendors use do not have different classification schemes. They all use CVSS Severity scores, go ahead and check.
Also definitions:
Firefox
Critical: Vulnerability can be used to run attacker code and install software, requiring no user interaction beyond normal browsing.
High: Vulnerability can be used to gather sensitive data from sites in other windows or inject data or code into those sites, requiring no more than normal browsing actions
Chrome
Critical:Allows an attacker run arbitrary code with the user's privileges in the normal course of browsing.
High: Allows an attacker to read or modify confidential data belonging to other web sites.
Also definitions:
Firefox Critical: Vulnerability can be used to run attacker code and install software, requiring no user interaction beyond normal browsing. High: Vulnerability can be used to gather sensitive data from sites in other windows or inject data or code into those sites, requiring no more than normal browsing actions
Chrome Critical:Allows an attacker run arbitrary code with the user's privileges in the normal course of browsing. High: Allows an attacker to read or modify confidential data belonging to other web sites.