If you can do that and it stays usable with 200% enlargement of fonts, it's actually meeting AA accessibility standards:

The scaling of content is primarily a user agent responsibility. User agents that satisfy UAAG 1.0 Checkpoint 4.1 allow users to configure text scale. The author's responsibility is to create Web content that does not prevent the user agent from scaling the content effectively. [w3.org]

I know Firefox lets you force a minimum font size for all pages, in addition to per-page zoom settings that it remembers.

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