Firebird is/was the early version of Firefox from Mozilla. I don't know if it's even still available :/

I kept it on the drive after first installing Firefox until I was happy that FF was going to be OK. I could launch either browser at the time. I have always found that FF updates install themselves invisibly, with all bookmarks intact.

I did have slowness, crash and hangup problems with websites containing Java applets until I updated Java (from Sun microsystems), then no more problems.

M.