Sorry, only one persdict.dat file is allowed or used per Firefox user Profile. You could create additional Profiles to have unique "personal dictionaries".

https://support.mozilla.com/en-US/kb/Profiles

Thanks for the reply.

I know this is not a forum for discussing addons or hacks to firefox.

I do not think I have a perdict.dat, and guess it is only created when words are added by firefox, and when an addon spellchecker is not in use.

I already use multiple OS accounts, and multiple firefox profiles in a single account. I may look at this later if the persdict.dat is plain text or csv it will be easy to edit, although that may be less straightforward if it is compressed data. I will possibly consider writing a .bat that rewrites it with chosen versions as a solution.

I have meanwhile markrd this as solved, as you did answer the initial question, Thanks.

PS I note that ticking 'solved' removes any 'Post a Reply' content

The persdict.dat file doesn't exist until the first "personal" spelling is saved. It is a custom text file, with one custom dictionary entry per line. Compression isn't used. It is easy to edit or add words by using a simple text editor, as long as the "one word per line" is kept intact, and special characters aren't added by the text program.

The same persdict.dat file )per Profile) will be used by any "dictionary" you have installed, and it is used by the Spellbound extension, too. As to other "spell check" extensions, I can't say - the built-in spellchecker suits my needs, although I did use Spellbound before Firefox included the spellchecker as a feature. Before Spellbound existed, I "rolled my own" spell check "extension" with instructions that were posted in the MozillaZine fora using files extracted from the Mozilla Suite (which is now known as SeaMonkey.)

Is there anyway I can setup a centrally located custom dictionary for my office that could keep all users' custom dictionary updated?