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Works like a charm. I recomend to set autozoom for every new tab.

Zoom Page WE reúne , informações, produtos e serviços para as novas gerações de empresas 100 % Digital, na nova era do trabalho, flexível, digital, sem papel, seguro e em todos lugares.

There are a lot of addons that imply a permanently open sidebar - Tree Style Tab (177k users), Simple Tab Groups (64k users), Sidebery (34k users), Tab Stash (21k users) and a bunch of others that are not related to tabs. In your addon, the "fit-to-window" image scaling mode still doesn't take into account the open sidebar. Your addon scales the image really "fit-to-window", but should scale them "fit-to-content-area-visible".
For all these hundreds of thousands of users, your "fit-to-window" mode is meaningless and useless.

I was ready to delete Firefox, and go back to Chrome because of its sub-standard zoom ability. Then I discovered Zoom Page WE, and I'm back to loving Firefox. They sorely need to incorporate the capabilities of this extension into Firefox!

Highly recommend! Very useful and flexible. You can customize size of page, font or both. Makes website easier to see and use.