Also looking for read only toggle. Before having edit access (which I do need sometimes), I would use the Z key shortcut to zoom in on specific areas. Now that I have edit access, no matter what tool I have selected, it types a Z out?
A huge plus 1 to this.
Good news: The solution to this has arrived decisively, in the form of 
Dev Mode. See https://www.figma.com/dev-mode/
“Dev Mode is like a browser inspector for your design file—simply hover and click objects to get details like measurements, specs, and styles—all within a safe space that won’t impact the design file.” 
To have a document you can fiddle with, make small changes to etc it’s probably still best to create a duplicate or branch.
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+1, keeping this topic open for votes
As admin of a few Figma teams, I have the same need. I want to have a look into some files, without accidentally changing something or updating the “last changed” timestamp. An “open read-only” mode would be needed.
Would be super useful to toggle read-only mode. I often have stakeholders (e.g. PM, dev) who are not very familiar with Figma and don’t watch the Figma tutorial videos, and it would be helpful to see what they are looking at, so that I can explain or send them screenshots.
dev mode doesn’t solve this problem - it only enhances the develop experience. the problem(s) this thread is describing is that files are open to manipulation by anyone with an editor seat in Figma. file owners should be able to lock down files they create so that only they can edit them. additionally, main branches should have ‘read only’ modes, so that the only editing that can be done has to go through branches.
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More than agree here.
This feature is highly needed. We are moving towards an Engineering-like workflow with Master files, branches and branch-reviews ; but this entire process is kind of useless if we can’t lock the master files or at least force them into read-only files.
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Today I’m using Figma for the first time for a new gig. As software engineer who will be implementing designs, this is literally one of the first things I googled about Figma. I don’t want to accidentally change something, especially as I’m unfamiliar with the shortcuts.
Very surprised this doesn’t exist as an easily accessible high-visibility feature.
I mostly like the solution of going into Dev mode because it’s quick and easy and requires no new functionality. In my particular case, seeing the connectors in prototype mode is really useful, and I don’t think that’s possible in dev mode. (It’s also very possible I’m missing something because I only just now learned this trick.)