I've heard that a domain name should not be longer than 26 characters
because some browsers may not accomidate it.

If so, which browsers - old versions of netscape and IE?

Does the 26 characters include the "www." prefix and the ".com"
suffix?

Thanks.

Hello Skip9801,
According to the websites I have gone to, the domain name limit was
not set by the browser version, but rather by the companies that
handle domain name registration. The 26 character limit was maintained
until around 1999, and then the 67 character limit was applied. No
reason is given for why there are limits though, I suppose they are
programming limitations in the same sense as the 8 characters for
filname and three for extensions in DOS. As for browsers, I suppose
any browsers can now use the 67 character limit, unless probably they
are very old browsers like IE 1.0. Lastly, the "www" and ".com" parts
are included in the limit.

Sources:
Domain Name Characteristics - Igoldrush.com
http://www.igoldrush.com/intro2b.htm

Internet Domain Registrars increases length of Internet domain names
(to 67characters)
http://archive.infoworld.com/articles/ic/xml/99/12/16/991216iclonger.xml
- This shows that Internet domain registration companies also set the
limits.

Long Domain Names - Domain Register.com
http://www.123-domain-register.com/longdomainnames.htm

Message thread discussing a problem with domain name + subsite URL
registration
http://frontier.userland.com/discuss/msgReader$9863?y=2002

Aerohost - Domain names - Reserve, register, park, domain names - FAQ
http://aerohost.com/domain-name-faq.htm

Domain name length - practical limits
http://www.dgl.com/msg4/messages/897.html
- Says here that some browsers support more than 26 characters for a
domain name.

Google search terms used:
domain name 26 character limit
domain name length limits
browsers support domain name length limit

I hope this has been a most helpful answer. If you have any problem
with it, do please post a Request for Clarification and I shall
respond as soon as I can. Thank you.

Good answer.  Concise, to the point, good background.

A great load of thanks for the five-star rating!