I was a Netscape user also and was forced to change due to new features being added to web sites that was no longer supported by Netscape. I now use Thunderbird version 2.0.0.19 and I am able to clean forwarded messages, sometimes with difficulty. I have no problem with deleting plain text, but sometimes have trouble with text within a 'frame' or graphic images. My work-around for this is to move to the bottom of the frame and begin deleting from the bottom, or right-click on it and delete the whole frame. Usually, I can start a selection from the bottom and delete that portion. If the 'text' is really an image, the entire image has to be deleted. If all else fails, as mentioned by a poster above, you can select, copy, and then paste into a new email window. By the way, I was able to import all my old email messages into Thunderbird (from Netscape), as well as my address book. Thunderbird appears a little different to Netscape, but most of all the features are there.

Have you made any progress?

IMAP works such that what you do in the client is reflected to the server, and vice versa. That's the point of it vs. POP3. Any messages you want to retain on the GMail server, you can't delete them from the (IMAP) GMail account tree in Thunderbird. I *never* keep long-term copies of mail on a server. It's *my* mail, I want it archived to *my* computer. IMO there's too much risk of a hacker getting access by brute-force or a server-side security flaw. My computer is more secure, less likely to be hacked, and I can back up the data. I have messages in Thunderbird that date 10 years back. And archived data MUCH older from Outlook Express.

I think that's one of those programs that people either love or hate. Not much in between. Here's a thread from an email forum on the subject. The site's email guru has a bit about his negative experience with the program (mainly its company's 'shady' practices). Take it FWIW. :-)