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Tried to upgrade as suggested. Firefox won't open now, says my Mac isn't a compatible version. How do I get the old Firefox system back?

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Went to open Firefox this morning. It said I should upgrade to the new Firefox. I downloaded as requested. When complete, I tried to open Firefox and it said the new version isn't compatible with my older Mac. How do I get the older version of Firefox on my system and get rid of the new one that won't open??

Went to open Firefox this morning. It said I should upgrade to the new Firefox. I downloaded as requested. When complete, I tried to open Firefox and it said the new version isn't compatible with my older Mac. How do I get the older version of Firefox on my system and get rid of the new one that won't open??

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