WRONG - K-Meleon 0.7.1 (SP1) which is based on Mozilla 1.2 uses 12 megabytes of disk space. Go to a DOS box a type dir /s \Program Files\K-Meleon
Mozilla does indeed use around 22 megabytes of disk space.
Opera uses less disk space because the executable files are compressed which is why zip.dll is present so this isn't even a fair comparison, if the Opera files were uncompressed then it would use a whole lot more disk space.
As for the M$-Borg(tm) browser, it uses the most disk space of all (and is the buggiest) but should really be removed from the system with IEradicator - http://www.litepc.com