This mode is really not much different than anonymously viewing the site (no edits or additions are allowed).
Most often, this is reserved for those who, for whatever reason, have lost their priviledge to post new bug reports. Initially, this is only a temporary measure to allow the user some time re-read the documents related to Rules & Regulations, FAQ and other things that all Testers need to know and apply in their reports. If you attempt to 'rejoin' as a reporter in another account while you are in this Viewer "time out" - this will more than likely cause your account and future accounts to be permanently set to Viewer, disallowing you from ever reporting bugs. If further incidents occur, complete banning from the site is to be expected.
This is the default level of access. It allows for a fair amount of interation to the site. You can create NEW Bug reports, Edit or Modify your own bug reports and add NOTES/Attachments to all NON-CLOSED Bug Reports.
Testers are to be respectful and humble towards all users on MAME Testers and follow direction set out in the Rules & Regulations page. While it may not sound like much, this is the most valuable asset to MAMETesters. Without accurate reports - Developers often will not notice a bug for a long time if ever at all. If a Tester is repeatedly warned about something either dealing with the quality of report or conduct and makes little effort to fix this, they may be set to Viewer status. (read Viewer information above).
Everything mentioned above for Testers are expected of the Senior Tester. You also get a few more privledges that normal Testers which include the ability to modify any bugs' specific information. By applying the Legend and Guidelines page information, your additional role is to be a "proofreader" for the newly reported bugs by ensuring correct information is being imparted. Items such as CATEGORY, SEVERITY, SOURCE and AFFECTED SETS are probably the most important to make sure are correct. Avoid making large amounts of changes to long standing bugs as it quickly pushes the new, unassigned bugs off the My View page.
MAME developers. They can be assigned to bugs and handle them.
Again, everything mentioned above is in effect. Your additional duties are to moderate the reports as they appear. Confirming or invalidating reports is probably the most common activity. It's good to remember that you should not immediately confirm your own report - another Moderator, Developer or Administrator should do this.
The rule of thumb is: If you can confirm a bug report that is not yours, CONFIRM it. If it is non-reproducable, it's best to leave the bug open for a time to allow other Testers an opportunity to confirm. Also, communication (largely in private) is expected from you to help those having trouble with producing useful reports to improve. While you have access to many Administrator functions, you are not to use them unless specifically directed to by the Administrator himself. This includes Account Modification/Deletion or any other Web-based adjustments.