...as a system admin, I oversee about a 50 Win7 computers now and NONE of them have any real issues with IE9 or Firefox.. And yes, all of the information given here is through each individual's experience and therefore, it IS their opinion.Since you've not given any specifics about WHAT TYPE of problems you're having, then it appears like you're giving your opinion as well..
As with the original poster in this thread, you've given us no information about your computer.. amount of RAM, type of internet connection, whether you've try uninstalling conflicting programs to troubleshoot the issue(antivirus, firewalls, etc.), plus "DOES NOT WORK WELL" isn't a real technical way of describing a problem...and as such, it's tough to know what to suggest as to answers..
Remember also, each user's computer configuration will be different, as will the types of programs they use.. I primarily deal with Windows 7 Pro computers on a commercial basis, but I also do side jobs for a handful of customers which also use Internet Explorer, Firefox, and the other browsers suggested in my first post. We've seen all the browsers at work and I use them all. We've had no substantive complaints about the general function of IE9 or Firefox on Windows 7. But that doesn't mean you aren't satisfied with their performance.
Since all the browsers are free, why not give them a try. The "lightest" one on your system will be Opera, but only you can say which one is best for you. Then YOU can give us YOUR opinion on which one you prefer, remembering to provide all information about the computer configuration, all the programs installed on it, and the types of websites you visit when using your browser. Each user's mileage will vary.
Hope this helps.
Grif