Hello ,

this problem could probably be caused by a Firefox extension.

To make sure that no extension is causing the problems, start Firefox in Safe Mode by following the instructions in the Diagnose Firefox issues using Troubleshoot Mode article.

Kind regards, Tobbi Firefox Support Volunteer

It does this in safe mode.

Create a new profile as a test to check if your current profile is causing the problems

See Basic Troubleshooting: Make a new profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins"

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files) See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Before I do that I have to ask if creating a new profile is any different than safe mode?

Creating a new profile does more than using safe mode. For example changes made to preferences remain in effect in safe mode. Creating a new profile will set everything back to default, and can help in situations where the problem still occurs in safe mode.

If the problem still occurs with a new profile, there are other troubleshooting options you can try. These are explained in the Troubleshoot and diagnose Firefox problems guide. In particular try the sections on troubleshooting plugins and then clean reinstall.

How many words are underlined when that happens?

There is a maximum (pref: extensions.spellcheck.inline.max-misspellings), but that is 500 by default, so you shouldn't hit that limit.

There is a maximum. I've also seen it happen on some occasions that words are no longer underlined, but if I type a new word wrong then that word gets underlined.

Only a short paragraph maybe 50 words.

I will try the new profile.

Has no one else seen this?