Browser windows dimming while active on MacBook Air

Hello folks,

Just recently I purchased a MacBook Air 13'' (1.7 GHz, 4GB, 256GB) with Lion installed in it and I have got an external monitor attached to it. It's been working really well for a couple of weeks, but in the last couple of days I have noticed how my browser windows, and only those!, for either FireFox, Chrome or Safari, keep dimming themselves while I am on other windows from other applications as if they were inactive, when they are not, because I am using the Mac still. And I can only get them to work again, i.e. loading Web sites, only after I click on them to activate them, which is annoying, because I may be on another window, would need to click on a link and it won't load on the browser window till I have clicked on it, on the browser window, that is.

I have searched in Google and found a couple of articles where it was highlighted how the problem may well be with the Settings under "Energy Saver" and I have got unticked in there for "Slightly dim the display when using this power source" and "Automatically reduce brightness before display goes to sleep" and still the same problem. Other articles suggested that I would try Caffeine and install it to get rid of the dimming of the screen, but even after installing I still have got the issues and I am, at this point, running out of ideas.

Does anyone know how to fix this issue and get things back working again? I am using latest versions of both Chrome and FireFox, the latter on v.11.

Thanks much in advance!

Regards

Luis