It's hard to understand you clearly, but as I do, you're getting random characters when "retrieving" the firmware through browser, do you?
That random characters "are" the firmware. Save the page onto disk. Just check that the file sizes are different for each mtd partition and double check each one with another downloaded copy, as every copy should be equal.
The browser should download a file, not a page, but it can happen when mime types are not correctly defined/retrieved. Anyway, you can save that page as a binary file.
The problem was due to the anti-virus, it does not allow you to download the firmware files to the router through a Web server, and now everything is OK. Now I need to burn these files to a different router that I need to fill in the router? Only mtd3 and mtd4?!
