User Agent: Mozilla/5.0 (Windows NT 6.1; rv:5.0) Gecko/20100101 Firefox/5.0 Build ID: 20110615151330 Steps to reproduce: I have a 2 monitor system with 1 (Faster/PCIe) ATI card and 1 (slower/PCI) nvidia card. The switch to version 5 slows down mouse movements to a crawl on the older nvidia card. I just have to move the window to the other screen and things are chugging along fine Actual results: As I move the mouse around, the window tries to highlight the current line (using CSS I guess). On the older card, this is excruciatingly slow. I can see each line being redrawn. On the newer card, it's relatively zippy Expected results: On the newer card, it's relatively zippy. I think the default theme needs some work, or an option to turn off tracking.

Just to confirm that all my video/system drivers are the latest ones and the issue did not exist in TB 3.x

Jacques does it work better if you disable hardware acceleration ?

In Tools > Options > Advanced > General, click Config Editor and modify the following related preferences (both and/or individually): * gfx.direct2d.disabled (double-click to change from "false" to "true") * layers.acceleration.disabled If that helps, it may be a duplicate of bug 668552.

(In reply to comment #3) > In Tools > Options > Advanced > General, click Config Editor and modify the > following related preferences (both and/or individually): > > * gfx.direct2d.disabled (double-click to change from "false" to "true") > * layers.acceleration.disabled > > If that helps, it may be a duplicate of bug 668552. The combination of these 2 settings have done the trick. I'm assuming they disable hardware acceleration and some kind of multi-layer rendering. Would love to know what they do. I tried them individually and no dice. You are right, this might be a duplicate of bug 668552 - I have not looked at the GPU usage (will download a widget later). Also there are new skins available for 5.0 I might try an alternative skin and see how that fares. Not sure on how to "dispose" of this bug (duplicate, resolved etc.)

Thanks for double-checking. I'll go ahead and mark this as a duplicate of the other one, given that the symptoms and workarounds fit that description. We can always reopen your bug if it turns out to have a different cause, but it's usually best to keep the discussion in a single place. > Would love to know what they do. Me too... ;-) it's a bit fuzzy, but certainly intended to utilize some features of the graphics card to optimize processing of fonts and graphics. The Direct2D part is specific to newer Windows platforms and an alternative to the older GDI rendering method, as far as I understand. Apparently it's too much load for some type of cards, or the card not accessed in the right way.

Confirmed duplicate of bug 668552. As a side note, on an alternative skin (Nuvola to be exact) - I only needed gfx.direct2d.disabled I guess that skin doesn't use layering.

Interesting observation, so this may be related to some feature the new aero theme is using...