Hi steeldrv, you can remove Firefox's certificate store file (cert9.db) and let it generate a new one. However, if you mention what is happening now -- do you get an insecure connection error page? -- there might be a different workaround.

For the steps to replace the cert9.db file, see the "corrupted certificate store" section of the following article: What do the security warning codes mean?

That article also lists possible fixes for other issues. To find the particular error code, you might need to click an "Advanced" button on the error page.

Did you try to close and restart Firefox? If you deleted builtin root certificates then this might help.