I have several user with light client (Browser) who use IE or Firefox and we have this error message since they had been updated (themselves…) in Firefox 3 :
This browser is currently not supported: Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv:1.9) Gecko/2008052906 Firefox/3.0
Supported
browsers: versions: platforms:
MS Internet Explorer: 5.5 or higher on MS Windows
Netscape Navigator: 4.7x on MS Windows or Linux
Subject: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
Firefox 3 has made more “security” fixes that break most applications using signed script. DWA uses signed script to implement capability not possible to previously do otherwise. See this Bugzilla posting to get a better understanding of what changed:428995 - signed script gets Permission denied when calling javascript from IFRAME (unsigned) - works with older firefox2
Aaargh! We’re working on figuring out how to cope with these changes.
Oh did I mention DWA (to be renamed Lotus iNotes) will support Safari with it’s 8.5 release (though officially qualified and supported only on Mac OS 10.5). 
Subject: RE: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
No offense to any Mac user (I am one as well), but Firefox (especially Firefox 3) is a far superior web browser to Safari. And seeing as Notes 8.5 will reportedly run on OSX the need for DWA support for Safari is really almost a moot point.
That being said, IBM/Lotus should focus their energies on making sure they support the two browsers they currently “support” before going after the third place browser.
Till such time Firefox 2 runs DWA superbly on OSX, Windows and Linux.
Subject: RE: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
Thanks for your post, I will follow the post on bugzilla.
Subject: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
Not that it really matters, but Firefox 2 wasn’t “really” supported under iNotes6.
More importantly though, Firefox 3 breaks much of the iNotes 7 functions including (but not limited to) adding attachments to e-mails and replying/forwarding e-mails that contain attachments.
Subject: RE: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
My users used Firefox 2 without problem before and not specially with iNotes but on all WEB databases.I have the same problem when I try to access to my WEBAdmin page :-(.
Subject: RE: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
you might want to report this to Mozilla
Subject: RE: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
I just do it
"You’ll need to get in touch with the software vendor regarding getting their software to support Firefox 3. They may already have an updated version which may work with the new browser. "
… 
Subject: FIREFOX 3 : This browser is currently not supported: Mozilla/5.0
It"s a standard… 11 000 000 download in 24 hours