It's great to hear Fx 3.5.7 is working well for you, David.
I don't particularly like using safe mode as it doesn't really find the problem, if you have 30 add-ons it wouldn't find if this was a conflict with a single one.
Also as polonus mentioned, some people are finding safe mode even less stable.
I find that removing the extensions cache files is rarely necessary, but always safe. It does have the side effect of enabling any disabled extensions and removing any of the compatibility updates. After an extensions cache file cleanout, I need to click Find Updates in the Extensions Manager. Compatibility updates doesn't need to download the extensions again. It just downloads the low bandwidth compatibility information, which is stored in one of the extensions cache files.
You're right. Firefox -safe-mode merely helps narrow the problem down. It doesn't tell you which extension, theme, or setting is causing the problem.
I think Polonus may be mistaken about Firefox -safe-mode being problematic in Fx 3.5.7. That would have been all over Mozillazine and the other Firefox support forums by now if it were the case. Any reports like that are usually caused by the user having other problems which aren't eliminated by safe mode. I've never heard of a situation where safe mode
caused problems. I doubt greatly that that's the case now.