What are these tiny plastic brackets inside my window frame?

Brackets to hold the bottom of vinyl blinds down. Keeps them from moving in the wind.

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There are a bunch of these clear plastic brackets around a large window dating back possibly to the 1980s or 1970s. I wasn't living here when the window was installed. Most of the brackets are broken. They've clearly been painted over several times and the colors tell me that it's been a couple decades at least because this place had been painted in those specific colors dating back to around then. I don't have any way to contact previous occupants or owners to ask them about what they could be.

The ruler is in inches.

I haven't seen anything like it at a hardware store, and I've looked quite a bit. They almost remind me of shelf brackets but these look way too weak to hold a shelf and there is no evidence of a "front half" of sorts further out to support that hypothesis. They are (were) screwed in with short screws through the large middle hole.

They kind of look like a guide to help the window stay in place when closed or maybe to reduce shudder in windy situations.

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So they were screwed through the rounded tab? Does the sharp-cornered tab have any holes? How many were there total? Were they only along the bottom? Sides? Top?

My first thought was brackets to hold blinds taut, as u/Medium-Ad8013 suggests, but the sort I've seen have a hole or a nubbin, to mate with an opposite nubbin or hole on the bottom of the blinds, but yours don't appear to have either which is the only reason I think that might not be right.

Need to see the window frame where they were.

Pella and others make a window with the mini blinds installed between the exterior glass and an interior glass panel. They stay cleaner that way.

Someone may have tried to create their own version of that by making those brackets to hold a pane of plexi or regular glass in place over the existing window sash.

Some parts look like blind holders and some look like sheet holders.

Solved! I found the product, it's a Prime-Line L5840 "screen fastener" for holding a window grid.