Cite an Online Forum?

Debbie, it appears that your first citation follows the bulleted list of elements given at 2.33 for websites that offer just one thing--i.e., the equivalent of a basic book. Look below that and you'll see the following:

"If the website offers multiple items by different creators ... it is the equivalent of a book with chapters by different authors. That calls for citations of two additional items:

• title of database, article, image collection, personal page, etc.;
• name of the item's creator

When we cite a chapter within a book or a database at a website that contains other materials (or an article in a journal), we always identify first the specific item we are using; then we cite the larger publication in which it appears

Name of Individual Author/Creator, "Title of Individual Item," Name of the Larger Publication, Title of the Larger Publication (Publication Data), specific info of interest.

The QuickCheck model that you followed on p. 789 (and many other examples throughout the book) demonstrate this pattern. Your second example follows it well. We would tinker with only one thing.  GenForum is the name of the website (which means italics are appropriate). Genealogy.com is the name of the company that created GenForum (hence, it should not be italicized.  I.e.:

Debbie, it appears that your first citation follows the order of the bulleted list of elements given at 2.33 for websites that offer just one thing--i.e., the equivalent of a basic book. Look below that and you'll see the following:

"If the website offers multiple items by different creators ... it is the equivalent of a book with chapters by different authors. That calls for citations of two additional items:

• title of database, article, image collection, personal page, etc.;
• name of the item's creator"

When we cite a chapter within a book or a database at a website that contains other materials (or an article in a journal), we always identify first the specific item we are using; then we cite the larger publication in which it appears

Name of Individual Author/Creator, "Title of Individual Item," Name of the Larger Publication, Title of the Larger Publication

The QuickCheck model on p. 789 (and many other examples throughout the book) demonstrate this pattern. Your second version of the citation follows it almost perfectly, with one exception.

• GenForum is the core website for these messages (and you have appropriately italicized it), but Genealogy.com is the company that created GenForum. The creator's name should not be italicized.

EE would also tinker in one other wee way. Well, two.

• In your citation "no. 246" goes unexplained. For clarity, the citation should identify what it represents.
• No comma should appear before the opening parens. The data that is in parens modifies what comes before it. Putting a comma between the two splices the two apart. In fact, there's a rule of thumb here that applies to virtually all types of writing: Parentheses should not be prefaced by a comma because a comma serves no function there. It's just extraneous punctuation.

All things considered, EE's tinkering would render this:

Association des Familles Pelletier, "Re: Pelletier siblings in Fall River, MA," discussion list, 24 May 1999, Genealogy.com, GenForum (http://genforum.genealogy.com : accessed 24 May 1999), message 246.

eevande, you certainly demonstrate the tumultuous nature of citations to online material. You also underscore why certain pieces of information are needed to help others retrieve material after a website has undergone an upheaval. 

There is another reason why "message number" is problematic in a dynamic forum such as this one. Anyone, at any time, can insert a new message immediately after an old one and thereby change all numbers from that point to the end of the thread.  

The date and time of the message is a viable substitute—even when a thread has 64 messages, as does the one you reference—because it's easy to scan the date:time stamp. On the other hand (as with citing any set of numbers), it's not failproof because someone can still make a typo and type, say, 15:12 rather than 14:12, or 28 September rather than 18 September.

As for whether you should (or may) add "/forums" after the base URL, that addition would help those who are not familiar with the organization of the website. On the other hand, since there are three different forums, you might be more specific. For example:

https://evidenceexplained.com/forums/citation-issues    (for the specific forum)

https://evidenceexplained.com/content/find-grave   (for the specific thread)

Specific URLs, of course, run the risk of going bad if the website is reorganized.  Here, let's knock on wood, but EE's website is just a few days short of five years old and, while we've upgraded numerous times, we haven't reorganized. (We did delete the online store, but there was no content there that would end up in citations.  Aside from that, the only other unworkable URLs have occurred when the website's distracted editor posts a link on Facebook without realizing that she was within the "administrative" mode when she copied the link—and, in those cases, someone usually straightens her out in a hurry.)