The ability to import data from an old Firefox profile would be nice too. I've been running Firefox a little without data importation for several years, so it now has its own set of data. I renamed the firefox folder under .mozilla as oldfirefox, and am running Firefox as if it's the first time now.

I don't know anything about Seamonkey data files. They probably have a forum where this question has come up.

How old is the old Firefox data? (Over the years, file formats change and the conversion code tends to get dropped after a while. Sometimes, in order to fully upconvert the data, you need to run the old profile in intermediate versions of Firefox.)

Problem not solved. jscher2000, we're talking firefox data no more than 3-4 years old, not going back 12 years. But Seamonkey's fine. At issue is how does current Firefox import current Seamonkey data. Seamonkey and Firefox nominally use the same codebase and datafiles. It ought to be not much more than a simple filecopy. But who knows anything about it? And why doesn't the import code still look for Seamonkey and its datafiles? There's no reason to have removed that code from Firefox.

Maybe I should take this to the Mozilla bugzilla site and report this as a Firefox bug.

Three years is a long time in browser evolution. But you can try a direct update and see what carries over. I suggest the "transplant" method described in the following thread. Two important changes:

(1) Your source folder will be different in Step 1. (2) You'll need to adapt my explanation from Windows to Linux in Step 2.

https://support.mozilla.org/en-US/questions/1322197#answer-1384732

You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder.

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager
  key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db
• cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words added to the spell checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

Can Seamonkey export bookmarks to html which you could then possibly import into Firefox?